A:唾液腺
B:甲状腺
C:汗腺
D:胰腺
— How long has the train been away?— Sorry. I don't know. By the time I got here, the train ________.
人类认识地球形状的过程依次是( )
S1____S2
S3____S4
S5____S6
七年级(3)班小奇同学进行研究性学习,他搜集了“贞观之治”“开元盛世”“玄奘西游”“鉴真东渡”的相关资料,由此推断他研究的课题是( )