In order to maintain a safe speed at all times，any necessary alterations of speed must（）.

A.be instantly put on

B.be instant put into use

C.be instantly put into effect

D.be put immediately

作为幼儿教师终身学习的内容有：（）

A.学习先进学前教育理论

B.了解国内外学前教育改革与发展的经验和做法

C.优化知识结构，提高文化素养

D.具有终身学习与持续发展的意识和能力