酶活力是指酶的
A．催化一定化学反应的能力B．改变一定化学反应的能力C．改变一定化学反应产物的能力D．重量单位E．重力单位
参考答案：A
30. --- Mrs. Smith, please teach me how to draw on the computer today.
--- Oh, no._______. You have to get familiar with the keyboard first.
A．It is never too old to learn
B．Think twice before you do
C．Learn to walk before you run
D．One today is worth two tomorrows
（）的逻辑关系式是：F=A+B（注：A和B为两个输入端，F为输出端）。
