what has happened 中为什么要用has 而不用have

what has happened 中为什么要用has 而不用have what has happened?为什么用HAS what happened what has happened No matter what ( )happened to you.用have还是has she has beautiful long hair.为什么用has而不用have My life has changed a lot!为什么用has而不用 have 为什么这里第三人称用have不用has My family has six members.为什么用has不用have our class has fifty students.为什么用has不用have what has happened是什么意思 what has happened? Do she have ···?为什么she后面不用has,而用have?