一期梅毒的潜伏期一般为（）
A.1～10天
B.2～3周
C.3～4周
D.1～3个月
E.3～6个月
参考答案：B
He could speak English fluently because he __________ it for four years when he was a college student.
A．had studied
B．have been studying
C．studied
D．was studying
散光
