● Either the mailman or the construction workers are causing Peggy to bark like crazy.

● Neither the dogs down the street nor the one next door pays any attention.

Compare this with the following:

● Either the construction workers or the mailman is causing Peggy to bark like crazy.

● Neither the one next door nor the dogs down the street pay any attention.

Agreement, in this case, depends on the placement of the subject. "Who," "which," and "that"

Remember dependent clauses? They have a subject and a verb, but they can't stand alone. That's what we're dealing with here, but with a little something extra. Now we've got to consider pronouns. A pronoun is a word that takes the place of a noun that comes before it, usually in the same clause or one very close to it.

　　Peggy is a troublemaker. She bites my ears and steals my food.

　　"Who," "which," and "that" are pronouns. When they take the place of a singular noun, they are singular; when they take the place of a plural noun, they are plural. This is important to remember when they are the subject of a clause. Compare the following sentences:

1. Big Dog is one of those animals who are very intelligent.

2. Big Dog is an animal who is very intelligent.

In both, who is the subject of a dependent clause. In number 1, it takes the place of animals (a plural form). That's why "are" is the correct verb choice. In number 2, who takes the place of animal (a singular form), and that's why "is" is correct.