根据赞可夫的研究认为；“一般发展”以( )为核心。
A．知识
B．能力
C．情感
D．智力
参考答案：D
按GB7588-2003《电梯制造与安装安全规范》规定，机房必须安装永久性人工照明，光照度应不小于（）lx。
A.50
B.100
C.150
D.200
By the time you ____ in, I ____ two letters.
A．had come, had written
B．came, wrote
C．come, have written
D．came, had written
