They had fun _____ games in the park.[ ]
A. play
B. playing
C. plays
D. played
答案:B
生态学是研究生物与______之间的科学。
酶原激活时,致使酶分子构象发生改变的原因是
A.氢键断裂B.肽键断裂C.疏水键断裂D.二硫键断裂