Agreement of verb 'to be' and a singular noun after a plural noun

Solution 1:

A subject can be plural while a complement is singular.

We (Mom, Dad, my sister, and I) are a family.

is a good example.

The computers are a good choice.

is the only correct one. Not just "righter".

You cannot use a singular verb for a plural subject (noun). In colloquial English, sometimes the constructions "we was" + [plural nouns] / "there is" + [plural nouns] are used. But this is only colloquial.

Solution 2:

Your example *"The computers is a good choice." does not sound right to me. However, "Computers is a good choice" is fine, as an answer to "What shall I study in school?" The "is" there is called "logical agreement", because the subject refers to a single area of study.

Is there a rule for when you can use logical singular agreement even though a subject noun is plural? Not so far as I know. Sometimes it sounds okay, sometimes not.