题目

分析一双链DNA分子时，发现30%的脱氧核苷酸含有胸腺嘧啶，由此可知中，胞嘧啶含量占总数的                                     A．20%        B．30%            C．40%          D．70% 答案：AThe new treatments ______by Norman Bethune helped a number of soldiers. A. invent          B. invents        C, inventing      D. invented