国产合金钢中的中合金钢，是指其合金元素的总含量（）。
A、3、5%~7%
B、3、5%~10%
C、5%~7%
D、5%~10%
参考答案：D
关于黄土高原的形成，已得到广泛支持的说法是
A．冰川侵蚀
B．岩层断裂
C．风力沉积
D．火山灰堆积
My sister _____ the league last month and she has decided to ______ the activities to help the aged in
town next week.
[ ]
A. joined; join in
B. joined in; join
C. attended; join
D. took part in; join in
