Learn French: L'équipe demande ce qui provoque ce phénomène. - The team asks what causes this phenomenon.

In indirect questions, you have to look at what role the word "what" plays in the second part of the sentence. Here, "what" is the subject doing the action (it is causing the phenomenon). When "what" is the subject of the indirect question, we use ce qui. If "what" was the object receiving the action (like in "what the team sees"), we would use ce que.

A team is a group of people, so why is the verb demande in the singular form?

In French, collective nouns like l'équipe (the team), la famille (the family), or le groupe (the group) are grammatically singular. Even though they represent multiple people, the word itself is singular, so it takes the third-person singular verb form just like il or elle.

Can I use the verb causer instead of provoquer?

Yes, you could say ce qui cause ce phénomène, and it would mean exactly the same thing. However, provoquer is very commonly used in French to mean "to cause," "to trigger," or "to bring about" an event, a reaction, or a phenomenon.

Why is it ce phénomène and not cet phénomène?

Phénomène is a masculine singular noun starting with a consonant. The demonstrative adjective (this/that) for masculine words starting with a consonant is ce. You only use cet before a masculine noun if it starts with a vowel or a mute h (like in cet homme).