题目

_______ good knowledge of several languages is essential to _____ study of comparative literature because without it one can read books only in translation.  A.  A; the           B. A;  /         C. The;  the            D. /; the 答案：A 解析: 略生物圈中已知的绿色植物有50余万种，他们形态各异，生活环境也有差别，可以分为四大类群：_______ 、_______ 、_______ 和_______