在( )m以下高度进行工作时，可使用牢固的梯子或高凳。
A．2
B．3
C．4
D．5
参考答案：B
In __________ review off 44 studies, American researchers found that men and women who ate six key foods daily cut the risk of __________ heart disease by 76%. _______
A．a; the
B．the; a
C．a; 不填
D．不填; a
600006000是由6个亿和6个千组成的．______．
