**Explanation:**
The correct answer is option B, "when".

In the given sentence, the phrase "I remember the day" indicates that the speaker is referring to a specific time in the past. The word "when" is used to introduce a clause that provides information about the time or situation in which an event occurred. In this case, "when" is used to introduce the clause "I met her".

Here is a breakdown of the options:

a) whom: This is a pronoun used to refer to the object of a verb or preposition. It is not appropriate in this context because it does not provide information about the time or situation.

b) when: This is an adverb used to introduce a clause that provides information about the time or situation in which an event occurred. It is the correct option in this sentence as it indicates the specific point in time when the speaker met her.

c) who: This is a pronoun used to refer to the subject of a sentence or clause. It is not appropriate in this context because it does not provide information about the time or situation.

d) which: This is a pronoun used to introduce a relative clause providing additional information about a noun. It is not appropriate in this context because it does not provide information about the time or situation.

Therefore, the correct answer is option B, "when", as it appropriately introduces the clause that provides information about the time the speaker met her.

Answer is "B" because the question is related to time! and while you are reading the question focused on what they are asking time, person, place, etc.. so this question is related to time so that "when" will be the Answer of this question!..