气焊、切割时使用输送气体的软管太长、太细，或者曲折太多易造成（）现象
A.自燃
B.爆炸
C.回火
参考答案：C
—— We’re organizing a party next Saturday, and I’d like you to come.
——_______! I have a meeting to attend that day.
A. Good luck B. What a pity C. Well done
镀镍是为了活化阳极镍板，镀液中一般不加入（）离子。
A、镍
B、硫酸根
C、硼酸根
D、氯
