由于蟹类的捕食,某种海洋蜗牛种群中具有较厚外壳的个体比例逐渐增加,对这个现象的解释,正确的是 [ ]
A.符合人类的需求
B.适者生存
C.定向变异
D.不用的器官逐渐退化
答案:B
It was foolish of him to _____ his notes during that important test, and as a result, he got punished. [ ]
A. refer to
B. stick to
C. come to
D. turn to
边滩