No, a singular noun cannot represent a plural non-collective noun. In English grammar, nouns and their corresponding verb forms should generally agree in number.

A singular noun refers to one person, place, thing, or idea, while a plural noun refers to more than one. For example:

Singular noun: "book"
Plural noun: "books"
In standard English, a singular noun should be paired with singular verb forms, and a plural noun should be paired with plural verb forms:

Singular: "The book is on the table."
Plural: "The books are on the table."
However, there are some irregular nouns, such as "sheep" or "deer," which have the same form for both singular and plural. In those cases, the noun itself does not change, but the verb form still needs to agree with the noun:

Singular: "The sheep is grazing in the field."
Plural: "The sheep are grazing in the field."
So, in general, a singular noun cannot represent a plural non-collective noun. Each noun should match its corresponding number in a sentence. https://blueskyconsultancy.com/ielts-institute/ielts-coaching-in-delhi/

In the sentence "I have two sons, Bill and Ben," a comma is more appropriate than a colon.

A comma is commonly used to separate items in a list or to provide additional information within a sentence. In this case, "Bill and Ben" are the additional pieces of information providing the names of the two sons. Thus, a comma is the appropriate punctuation mark to use.

A colon, on the other hand, is typically used to introduce a list, an explanation, or a quotation. It suggests that what follows the colon is directly related to or elaborates upon what precedes it. Since the sentence "I have two sons" does not require an explanation or a list, a colon would not be suitable in this context.

Therefore, the correct punctuation for your sentence is: "I have two sons, Bill and Ben." ielts coaching in delhi

https://www.oxfordlearnersdictionaries.com/grammar/online-grammar/past-perfect-simple-with-time-expressions#:~:text=We%20can%20use%20past%20simple,then%20the%20party%20could%20start.)

When using the past perfect tense with "until" or "before," we typically express an action that was completed or occurred before a specific point in the past. Here's how you can construct sentences using the past perfect tense with "until" or "before":

Until:

Subject + had + past participle + until + specific point in the past.
Example: She had studied until midnight before the exam.

In this sentence, the action of studying (past perfect tense: had studied) was completed before the specific point in the past (until midnight).

Before:

Subject + had + past participle + before + specific point in the past.
Example: They had already left before I arrived.

Here, the action of leaving (past perfect tense: had left) occurred before the specific point in the past (before I arrived).