皮亚杰认为，守恒是______阶段儿童具备的能力。

填空题智力是个体先天禀赋和______互相作用的结果。

填空题元认知策略包括监控策略、调节策略和______。

单项选择题Scientists say it may be a few years（）it is possible to test the new medicine on patient.

A. because
B. after
C. before
D. since

单项选择题The boy spends at least as much time reading as he （）

A. writes
B. is writing
C. does to write
D. does writing

单项选择题— What was he doing at this time yesterday — He （） to sing a song in English.

A. was trying
B. is tried
C. is trying
D. was tried