熔化极气体保护焊用的焊丝不包括（）。
A.实心焊丝
B.药芯焊丝
C.空心焊丝
参考答案：C
The country life he was accustomed to ________a lot since 1998.[ ]
A. change
B. has changed
C. changing
D. had changed
Jackson方法是一种面向______的结构化方法。
