Choose from the options lettered A - E the one that most appropriately completes each sentence __________ are not allowed into the premises.

Analyze the question: The sentence needs the correct plural form of the compound noun "passer-by", used as the subject of the sentence: "__ are not allowed into the premises."

Concept: In compound nouns made of a noun plus an adverb or preposition (passer-by, runner-up, mother-in-law), the main noun takes the plural "s". The adverb or preposition ("by") stays unchanged.

• passer-by → passers-by
• runner-up → runners-up
• looker-on → lookers-on

An apostrophe is needed only for possession (e.g. "the passers-by's complaints"). Here nothing is owned, so no apostrophe is needed.

Step by step:

1. The subject refers to more than one person, since the verb is "are". So we need the plural: passers by.
2. There is no possession, so no apostrophe.
3. Check each option: • A. Passer's by: wrong, because the apostrophe-s is misplaced and it is not a plural. • B. Passers' by: wrong, because the apostrophe is not needed. • C. Passers by's: wrong, because the "s" is on the wrong word. • D. Passers by: correct plural form with no apostrophe. • E. Passer by's: wrong, because it is not a plural and the apostrophe is misplaced.

Answer: Passers by (option D). Written properly, it is "passers-by".

Tip: For compound nouns, pluralize the important word (the noun), not the little word that follows. Think "mothers-in-law", "runners-up", "passers-by". Also ask yourself whether anything is being owned. If not, leave out the apostrophe.