计划生育药具管理机构应当指导育龄夫妻安全使用计划生育药具,()做好随访服务。
A.有时
B.随时
C.经常
D.定期
参考答案:D
________of recent political developments, he was taken by surprise upon his arrival in the capital.
A.Unexpected
B.Unacquainted
C.Unaware
D.Unknowing
传统磁铁催化剂中,当Fe2+/Fe3+等于或接近0.5时,催化剂还原后的活性最好。