换向阀换向是通过改变阀芯和阀体的相对位置来实现的。
A. 对
B. 错
We are taught that a business letter should be written in a formal style___ in a personal style.
A. rather than
B. other than
C. better than
D. less than
Do you regret paying__ as five hundred dollars for the painting ?”“No, I would gladly have paid for it.”
A. twice so much
B. twice as much
C. as much twice
D. so much twice
微信支付 
支付宝支付