题目

Many a professor _____ looking forward to visiting Germany now．Many scientists _____ studied animals and plants in the last two years. A．is; have        B．is; has            C．are; have          D．is; are 答案：A关于蛋白酶的叙述，不正确的是（  ）A．蛋白酶是蛋白质B．蛋白酶可以在细胞内、外起作用C．蛋白酶只能水解蛋白质D．蛋白酶的最适pH值是1.9