Self-study
Most lecturers who are effective teachers are eccentric, but some noneccentric lecturers are very effective teachers. ██ █████████ █████ █████████ ███████ ██ █ ████ █████████████
Summary
Most lecturers who are effective teachers are eccentric. Some noneccentric lecturers are effective teachers. Every effective teacher is a good communicator.
Notable Valid Inferences
Since we know that all effective teachers are good communicators, if we learn about some other quality that some or most effective teachers have, then we can infer that at least some people who are good communicators have that quality. This is why we can infer that some good communicators are eccentric and some good communicators are noneccentric.
9.
Which one of the following ██████████ ███████ █████████ ████ ███ ██████████ ██████
a
Some good communicators ███ ██████████
Must be true. Most lecturers who are effective teachers are eccentric and every effective teacher is a good communicator. There must be some overlap between good communicators and eccentric people, because we know there are at least some lecturers who are both eccentric and good communicators.
b
All good communicators ███ █████████ █████████
Could be false. This answer choice confuses sufficiency for necessity. We know that all effective teachers are good communicators, but that doesn't imply that all good communicators are effective teachers.
c
Some lecturers who ███ ███ █████████ ████████ ███ ███ ██████████
Could be false. We have a fact about lecturers who are effective teachers. But we don't know anything about lecturers who are not effective teachers.
d
Most lecturers who ███ ████ █████████████ ███ ██████████
Could be false. We can conclude that some lecturers who are good communicators are eccentric. But we don't know that most of them are. This is because the group of people who are good communicators could be so much larger than the eccentric lecturers that are good communicators. Most of the good communicators could be noneccentric.
e
Some noneccentric lecturers ███ █████████ ████████ ███ ███ ███ ████ ██████████████
Must be false. We know that every effective teacher is a good communicator. It is impossible for some effective teachers to not be good communicators.