企业税前加计扣除的委托外部研究开发费用，高新认定时按实际发生额（）计算纳入研发费用总额。
A.80%
B.60%
C.50%
D.40%
参考答案：A
Jimmy needs to improve his technique if he _____ gold at 2012 Olympic. [ ]
A. wins
B. is winning
C. will win
D. is to win
酶原为何无活性？酶原激活的原理是什么？有何生理意义？
