Self-paced
Superconductors are substances that conduct electricity without resistance at low temperatures. █████ ████ ████████ ████ █████ ██ ████████████ █████████ ██████ █████ ██ █ █████████ ████ █████████████ ██ █ ███████████ █████ █████ ███ ███████ ████████ ██ █████ ██ ████ █ ██████████ ████ █████████ ████ ██ ██ █████ ██ ███████ ███ ██████████ ██████████████ ████ ██████ ████████████ ██ ████████████ ██ ██████ ████ █████ ███ ███████ ████████
Stimulus Summary
"Use will never be economically feasible unless there is a substance that superconducts above minus 148" means feasibility requires such a substance. So: if the use of superconductors is economically feasible, then some substance superconducts above minus 148 degrees.
The third sentence: if such a substance exists, it must be an alloy of niobium and germanium.
The fourth sentence: those alloys superconduct at temperatures no higher than minus 160 degrees. Minus 160 is colder than minus 148, so "no higher than minus 160" means the alloys never superconduct above minus 148.
Anticipation
Suppose a substance that superconducts above minus 148 did exist. The third sentence says it would have to be a niobium-germanium alloy. But the fourth sentence says those alloys top out at minus 160, well short of minus 148. This means no substance superconducts above minus 148 at all.
colderwarmer
-160°C
-148°C
The alloy stops at -160°C, which is colder than -148°C, so it never reaches the zone economically feasibility requires.
With no substance superconducting above minus 148, nothing meets the economic feasibility requirement. So the use of superconductors will never be economically feasible.
7.
If the statements above are █████ █████ ███ ██ ███ █████████ ████ ████ ██ █████
a
The use of ███████████████ ████ █████ ██ ████████████ █████████
(A) must be true. Economic feasibility requires a substance that superconducts above minus 148. The only thing that could be such a substance is a niobium-germanium alloy, and those alloys never get above minus 148. So no qualifying substance exists, the requirement for economic feasibility can never be met, and the use of superconductors will never be economically feasible.
b
If the alloys ██ ███████ ███ █████████ ██ ███ ████████████ ██ ████████████ █████ █████ ███ ███████ ████████ ████ █████ ███ █████ ██████████ ████ ████ ██ ███
(B) is contradicted by the third sentence. The stimulus says that if any substance superconducts above minus 148, it must be a niobium-germanium alloy. So if those alloys can't do it, then nothing can. There are no "other substances" that will superconduct at temperatures above minus 148.
c
The use of ███████████████ █████ ██ ████████████ ████████ ██ █████ ██ █ █████████ ████ █████████████ ██ ████████████ █████ █████ ███ ███████ ████████
Economic feasibility needs a substance that superconducts above minus 148, but (C) offers one that superconducts below minus 148. A substance that only works below minus 148 doesn't meet the requirement, so it can't make feasibility possible. The stimulus has already shown economic feasibility can never happen, so nothing could bring it about.
d
Alloys of niobium ███ █████████ ██ ███ ████████████ ██ ████████████ █████ █████ ███ ███████ ████████
(D) mixes up what the fourth sentence says. "Superconduct at temperatures no higher than minus 160" means the alloys work at minus 160 and colder, so below minus 160 is exactly where they do superconduct. (D) claims they don't superconduct below minus 160, which is backwards. It would be correct if it said they don't superconduct above minus 160.
e
No use of ██████ ██ ███████ ███ █████████ ████ ████ ██ ████████████ █████████
The stimulus tells us only that using these alloys won't make superconductor use economically feasible. It says nothing about whether the alloys are economically feasible for other purposes, like ordinary wiring or manufacturing. So we can't conclude that no use of them will ever be feasible.