题干
—Alvin，are you coming with us?
—I'd love to，but something unexpected ________.
A：has come up
B：was coming up
C：had come up
D：would come up
答案(点此获取答案解析）
A
的焦点为F，准线为
,P为抛物线上一点,PA⊥
,那么|PF|=………………………………………………………………………………………… （ ）