短文改错。

     This morning I got up early and went to school as usually, only to find there were nobody in the

classroom because it is Sunday. "How a bad memory I have!" I couldn't help laughing. Stand in

front of the school gate, I began to wonder what to do next. Suddenly a good idea occurs to me.

"Why not get together with some good friends for a picnic in such a fine weather?" I immediately

telephoned some of my best friends, but they all agreed to join me. About two hours late, we finally

arrived a pleasant park with trees and flowers here and there. We really enjoyed us greatly.

长期使用会造成牙色素沉积的药物牙膏是

A．“全效”牙膏

B．洗必泰牙膏

C．脱敏牙膏

D．氟化亚锡牙膏

E．增白牙膏