尝试—错误学习的基本规律有( )。
A.效果律
B.练习律
C.准备律
D.尝试律
参考答案:A,B,C
解析:尝试一错误学习的基本规律是效果律、练习律和准备律。
When travelling, you are advised to take travellers' checks, which provide a secure ______ to carrying your money in cash.
A.substitute
B.selection
C.preference
D.alternative
修做梢土后戗时,地基清好后,在堤脚拟修后戗处的地面上铺梢料厚约()。
A.15cm
B.20cm
C.25cm
D.30cm