1. I met Tom in the park yesterday.

2. It was I that met Tom in the park yesterday.

3. It was I who met Tom in the park yesterday.

(What is the part of speech of 'that' in Sentence 2? Can we use 'who' instead of 'that'? Can we omit 'that'?)

4. It was in the park that/when I met Tom yesterday.
(Can we use 'when' instead of 'that'? Are both the same?)

2, 3, and 4 are awkward and too wordy. The first sentence is much better.

In sentence 2 "that" is a pronoun, but is not correct. When referring to a person, we use "who."

4. "That" is o.k., but "when" is wrong because it means time, not location. You could use "where" instead of "that."

1. "That" in sentence 2 is a relative pronoun.

2. Yes, you can use "who" instead of "that" in sentence 2. Both "who" and "that" can be used as relative pronouns referring to a person. In this case, "who" is more commonly used to introduce a relative clause referring to a person, while "that" can be used for both people and things.

3. Yes, you can omit "that" in both sentences 2 and 3. The sentence would still be grammatically correct and retain the same meaning. Here's the revised sentence: "It was I who met Tom in the park yesterday."

4. Yes, you can use "when" instead of "that" in sentence 4, but it would slightly change the meaning. "That" emphasizes the location where the meeting occurred, while "when" emphasizes the time of the meeting. So, using "when" would imply that you met Tom yesterday, regardless of the location, while using "that" specifies that the meeting took place in the park.