Self-study
Humankind would not have survived, as it clearly has, if our ancestors had not been motivated by the desire to sacrifice themselves when doing so would ensure the survival of their children or other close relatives. ███ █████ ████ ████ ████ ██ █████████ ██ █ ████ ██ █████████ ██ ███████ ████ ███ █████████ ████ ██ █████ █████████ ███████████
Method of Reasoning
The argument proceeds by establishing two conditional relationships:
(1) If our ancestors were not motivated by the desire to sacrifice themselves, humanity wouldn’t have survived.
(2) If our ancestors were motivated to sacrifice themselves, then they were behaving altruistically.
It then takes the contrapositive of the first statement to create a conditional chain, before validly concluding that the presence of the first sufficient condition (our ancestors surviving) implies the presence of the last necessary condition (our ancestors being altruistic). 
17.
Which one of the following █████████ ██ ████ ███████ ██ ███ █████████ ██ ███ ████████ ██████
a
Students do not █████ █████ ██████ ██ ████ ██ ███ ████████ ███ ██████ ██ ████ ████ █████ █████████ █████████ █████ ████ ████████ ████ ████ ███████████ ████████ ████ ████████ ██ █████ █████ ███████ ██ ████ ████████ ██████ █████ ████ █████
The argument proceeds by establishing two conditional relationships:
(1) If students do not increase their study time, then they will not raise their grades.
(2) If students do increase their study time, then they have good time management.
It then takes the contrapositive of the first statement to create a conditional chain, before validly concluding that the presence of the first sufficient condition (students raising their grades) implies the presence of the last necessary condition (students having good time management).
b
Organisms are capable ██ █████████████ █████ ███ ████████████ ██████ ██ ████ ██ ███ ███████ █████ █████████ ██ ██████ ███ ██ ██████ ████ ███████ ███████ ████ ██ █████████ ██ ███████████████ ███ █████ ██ █████ ████ ██████ ███████ █████ ████████████ █████████
Mismatched premises and conclusion. (B) presents a single conditional statement as a premise (if plants do not consume organisms, then they can produce their own energy). It then invalidly concludes that the absence of the sufficient condition implies the absence of the necessary condition. The stimulus, meanwhile, presents two conditional statements in a chain to reach a valid conclusion, so (B) doesn’t match.
c
If fragile ecosystems ███ ███ █████████ ██ ██████████ ██████ █████ ███████ ███████ ████ ███████ ███ ███████ ███████ ███ ██ ██████████ █████ ████ █████ ███████ ████ ███ ██ █████ ███████████
Mismatched premises and conclusion. (C) presents the definition of a term (endemic species), then creates a conditional conclusion based on this definition. The stimulus, meanwhile, presents two conditional statements in a chain to reach a valid conclusion, so (C) doesn’t match.
d
The natural resources ████ ██ █████ ██████ ████ ██ ████████ ██ ████ ███ ███ ████████ ██ ███████████ ██████████ ███ █████ ████ ███████████ █████████ ████████ ████ ██████ ███ █████████ ████ ██ ██████ ████ █████ ████ ██████ █████████
Mismatched conclusion. (D) Presents two conditional statements that can be chained to read Not Depleted→Replaced→More Power. Instead of concluding that the first sufficient condition leads to the last necessary condition, however, the conclusion incorrectly brings up the new idea of power being depleted. The stimulus, meanwhile, features a valid reading of a conditional chain, so (D) doesn’t match.
e
Public buildings do ███ █████████ ████ █████ ████████████ ██ ████ ███ ███ ████ █████████ ███ ███ █████████████ ████████ ██ █████████ ██ ██████████ █████ ██████ ██████ █████████ ███ █████████ ██ █████████ ██ ████ ████ ██ ███ █████████ ████ █████ █████████████
Mismatched conclusion. (E) Presents two conditional statements that can be chained to read Harmonize→Well-Designed→Expensive. Instead of concluding that the first sufficient condition leads to the last necessary condition, however, (E) incorrectly claims that either the last necessary condition must be absent or the first sufficient condition must be absent. The stimulus, meanwhile, features a valid reading of a conditional chain, so (E) doesn’t match.