1. Have you checked out our school website lately?

2. Have you lately checked out our school website?
(What is the suitable position of the adverb 'lately'?)

3. Is there something that/which I should see?
(Do you prefer 'which' to 'that' in this sentence?)

4. Mina sent me a message that she uploaded the pictures.
('a mesage' and the that clause is in apposition, right? What is the part of speech of the that clause? Is the that clause a noun clause or an adjective clause which modify 'a message'?)

#1 is far better than #2. Usually, adverbs should be as close to the verb as possible, but not with a phrasal verb and not before the phrasal verb.

For #3, I'd just skip "that" or "which" entirely! But if you need to use one, then use "that."

The "that" clause in 4 is a noun clause, and yes, serving in apposition to "message." In the "that" clause, however, I'd say "had uploaded" since the main verb is already in the simple past.

1. The suitable position for the adverb "lately" in the sentence "Have you checked out our school website lately?" is at the end of the sentence. So the correct sentence would be: "Have you checked out our school website lately?"

2. The adverb "lately" can also be placed before the main verb in the sentence "Have you lately checked out our school website?" Both positions are grammatically acceptable, but the typical placement is at the end.

3. Both "that" and "which" can be used in the sentence "Is there something that/which I should see?" The choice between them depends on whether the speaker wants to specify or restrict the options. "That" is used when the speaker wants to indicate a specific thing or a specific group of things, while "which" is used when the speaker wants to provide additional, non-restrictive information about something.

4. In the sentence "Mina sent me a message that she uploaded the pictures," the "that" clause is functioning as a noun clause. It functions as the direct object of the main clause. The entire clause "that she uploaded the pictures" is acting as a single noun, specifying the content of the message. Therefore, the "that" clause is a noun clause and not an adjective clause modifying "a message."