The following sentences ("incorrect" versions) despite not making as much sense as the correct (according to the quiz) alternatives, still make enough sense/are correct in terms of grammar, right?
Just adding a note to the last question. Best to use the english version to guide you in picking the answer. In this case, "I am his significant other". Grammar is correct in your sentence arrangement, but your arrangement's meaning is "My lover is him". So it is not the answer the question is looking for.