used for saying that one of two things has to happen or be true 要么…要么(表示两件事中必然有一件要发生或是真的) Either you come with us, or you stay at home with your mother. 要么你和我们一起去,要么你呆在家里陪妈妈。
Either he forgot about the meeting or he deliberately stayed away – I don't know which. 要么是他忘了要开会,要么是他故意躲开,我不清楚是哪一种情况。