writing question SAT

Can somebody tell me why for this question,

The automobile, the personal computer, the cell phone, – none (of these inventions) (were) (popular) among the public when (they were) first introduced. (No error)

(they were) is wrong?

Also, for this question,
Everyone is excited about graduation because all had worked so hard for it. No error.
Why is “all” considered wrong?

It should be None of these inventions was …

None takes Singular.

@cfcsjmishra None in that case is plural because the preposition phrase that comes after has a plural noun, inventions. However, I don’t understand why none is considered singular in the latter part of the sentence

From the American Heritage Dictionary: “The choice between a singular or plural verb depends on the desired effect.  Both options are acceptable in this sentence:  None of the conspirators has (or have) been brought to trial.”

The automobile, the personal computer, the cell phone, – none (of these inventions) (were) (popular) among the public when (they were) first introduced. (No error)
“none of these inventions were popular”=
“none of these inventions was popular”=
“neither of these inventions was popular”.

The introductions of those three technological marvels happened at different times, so it would make sense to indicate that fact by saying “when each of them was first introduced”. Makes a really awkward-sounding - but grammatically correct - sentence:
The automobile, the personal computer, the cell phone, – none (of these inventions) (were) (popular) among the public when [each of them] was first introduced.

Compare to the question from the Blue Book:
The Empire State Building, the Sears Tower, the Canadian National Tower—each (of these structures) (was) the (tallest) in the world at the time (they were) built. (No error)
Answer (D).

I don’t get this question.

Can someone explain it to me ?