目前我国普遍使用的伤寒疫苗为（）.
A.Ty21a减毒活菌苗
B.全菌灭活疫苗
C.类毒素疫苗
D.Vi疫苗
E.三联疫苗
参考答案：D
She ought to stop working; she has a headache because she ________ too long.
A．has been reading
B．had read
C．is reading
D．read
