Small experimental vacuum tubes can operate in heat that makes semicon

Vacuum tubes can resist more heat than semiconductor components.
A component whose resistance to heat is more will be preferable but only if it is comparable in other respects too such as maximum current capacity.
Vacuum tubes current capacity is not comparable yet.

Which of the following is a conclusion?

(A) Vacuum tubes are not now preferable to semiconductors for use in digital circuits.

Vacuum tubes are not comparable in other respects. It is not comparable in maximum current capacity. Hence they are not preferable to semiconductors. This is correct.

(B) Once vacuum tubes and semiconductors have comparable maximum current capacity, vacuum tubes will be used in some digital circuits.

We don't know that. Maximum current capacity is just one of the "other respects". Is it comparable in other "other respects" too? We don't know.

(C) The only reason that vacuum tubes are not now used in digital circuits is that vacuum tubes’ maximum current capacity is too low.

Again, is this the ONLY reason? Is it comparable in "other respects"? This may not be the "only reason".

(D) Semiconductors will always be preferable to vacuum tubes for use in many applications other than digital circuits.

Not known what will happen in the future.

(E) Resistance to heat is the only advantage that vacuum tubes have over semiconductors.

Not known from the argument.

Answer (A)