His English ________ a lot since he took the course.

A．improved

B．was improved

C．has improved

D．has been improved

平均利润率：就是剩余价值总量和资本总额的比率。据此定义，平均利润率的形成是()

A．资本家之间协商的结果
B．资本家垄断的结果
C．同一部门各个资本家之间竞争的结果
D．不同部门之间各个资本家竞争的结果