英文文法問是, is, are

a lot of 不同 a pile of

A lot of = many/much

“A lot of” is rather informal. It is used mainly before singular uncountable noun and plural nouns and before pronouns. It is the subject and not the form “a lot of” that makes a following verb singular or plural. When a lot of is used before a plural subject, the verb is plural; when a lot of is used before a singular subject, the verb is singular.

“Sheep” is a countable noun. The plural form of “sheep” is “sheep”.

There are a lot of sheep in the hut. = There are many sheep in the hut.

Sheep is plural in the above sentence. A plural subject requires a plural verb.

There is a lot of traffic in the city.
(traffic - an uncountable noun; a singular subject)

Pile (countable noun) = a group of several things of the same type that are put on top of each other.
A pile of things (things is a plural noun)

It is very important to identify the subject. The verb may mistakenly agree with a word that is not the actual subject. “of books“ is a prepositional phrase. Do not make the verb agree with the object of preposition. “books” is not the subject of the sentence.

There is a pile of books on the table.
The subject is “a pile”, not books.

Another example:
One of the boys is absent today. (“One” is the subject, not “boys”)