商品最本质的因素是（）
A.使用价值
B.交换价值
C.价值
D.效用
参考答案：C
违约责任也称违反合同的______，是指当事人因违反______而应承担的责任。
The club I____ and their club will unite to ____ the competition against the team from Wuhan. [ ]
A. joined, take part
B. joined in, attend
C. joined, join in
D. attended, take part in
