The correct answer would be 2, since the past participle tense of "get" is "have got". However, it is true that some Americans use "have gotten", although it is not the most orthodox one. Cheers!

Hello, Mona! Here are the examples for all 3 answers: 1. If I have a larger number of questionnaires returned, I will get more useful data. 2. If I'd had a larger number of questionnaires returned, I would have got more useful data. 3. If I'd had a larger number of questionnaires returned, I would have gotten more useful data. Hopefully, this helps you!

Grammatically speaking, both 2 and 3 are correct, but I hear a lot of American saying "I would have gotten" when they assume with "if I would~". You need " would" because you are assuming a situation which may not happen to you. So for example, If I were a super hero, I would do ~~. Remember this grammatical expression!:) If I were~, I would do ~~

Even as an English person, I'm not 100% sure of the answer. You'll be understood if either is used, however I think a British person is more likely to use "got" and an American is more likely to use "gotten."

https://www.englisch-hilfen.de/en/grammar/if_type3.htm i think there is the answer