I know the below sentence is not correct: Wrong: Hubieron cuatrocientos y treinta mils personas la asistieron. Someone has made it in this way: Grammatically correct: Fueron cuatrocientas treinta mil personas las que asistieron. There is a better way to say it: Correct: Se manifestaron cuatrocientas treinta mil personas. My questions are: 1. "Hubieron" is the past tense form of "hay", in English means "there is...". I wonder why it is incorrect. 2. Why should we use "fueron" (Ser) here? What does it mean in English? Thanks for helping me in advance.