Here are some points to remember about predicate pronouns.
1. Predicate pronouns follow linking verbs such as am, is, are, was, were, shall be, and will be.
2. A predicate pronoun renames, or refers to, the subject of the sentence.
3. A sentence with a predicate pronoun will usually make sense if the subject and the predicate pronoun are reversed.
The kicker was HE.
HE was the kicker.
Always use subject forms of pronouns for subjects and predicate pronouns.
INCORRECT: The runner was HER.
CORRECT: The runner was SHE
Based on that, the sheet evidently expected these ludicrously archaic and unidiomatic answers:
2. The most excited spectators were we.
7. The dog trainer we admired the most was she.
10. The best hockey player on the team was she.
12. The man slicing green beans for dinner is he.
Those are pretty weird, and I doubt any native English speaker on Planet Earth would spontaneously use such sentences. Nearly a decade ago, Pullum & Huddleston's The Cambridge Grammar of the English Language recently came out vigorously against forms such as "It is I" that use nominative pronouns in object position, noting them to be stuffy and highly formal to the majority of speakers. The sheet, however, falls into exactly the prescriptive error described in their A Student's Introduction to English Grammar (see pages 4-5): teaching an unusually formal (if not sufficiently unidiomatic to be outright wrong) construction as simply "correct".
As far as I can tell, in the USA at least, the prescriptive rule on predicate pronouns was stated most explicitly in grammar texts of the late 19th and very early 20th century, notably in the 1899 A First Manual of Composition and the 1902 A Text-book of Applied English Grammar by the prolific writer and rhetorician Edwin Herbert Lewis (Ph. D., LL. D.,. Professor of English, Lewis Institute, Chicago).
It's I. / It's they.
It's he. / It's who.
It's she. / I thought it was he.
It's we. / I fear it's I whom you mean.
So the subject-pronouns and the predicate-pronouns are the same.
In conversation it is permissible to say It's me, but It's I is better.
- A First Manual of Composition
In answer to the question "Who is it?" we are permitted to say " It's me," instead of "It is I." But it is just as simple to answer merely the word "I." Such questions as "Was it I that you wanted?" are very common among correct speakers, and are not pretentious. But even if we allow ourselves to say "It's me," we must not allow ourselves to say "it's him," "it's her," "it's them." These are vulgarisms.
- A Text-book of Applied English Grammar
Now, a over century later, this advice is hopelessly outdated. As the press release for The Cambridge Grammar of the English Language put it:
Myth: Expressions like "It was me" and "She was taller than him" are incorrect; the correct forms are "It was I" and "She was taller than he."
Pullum responds: The forms with nominative pronouns sound ridiculously stuffy today. In present-day English, the copular verb takes accusative pronoun complements and so does "than." My advice would be this: If someone knocks at your door, and you say "Who's there?" and what you hear in response is "It is I," don't let them in. It's no one you want to know.
- Monumental New English Book Helps Debunk Grammar "Rules"
Googling tracks the content of the worksheet in question to this document on the TeachersWeb site for the Language Arts department of Bella Vista Middle School, California. The fine print credits it to "McDougal, Littell & Company" - now merged into Holt McDougal, a division of Houghton Mifflin Harcourt Publishing Company.