—Did you hear someone knock at the door just now?
—Sorry, I ______ to my friend on the phone.
A：was talking
B：talked
C：am talking
下列各句中加线的成语，使用恰当的一句是( )
下列函数中，是二次函数的是（ ）
The old man keeps walking around this street. I think he is new here and now he has trouble ____ (find) his way.
