题目

As I will be away for at least a year. I’d appreciate hearing from you telling me _____how everyone is getting along. A.     By and by  B. more or less  C. now and then  D. at the same time 答案：C 解析: ：by and by意为before long即不久以后；more or less意为或多或少表数量 now and then意为from time to time时而，表频度，此处修饰telling 发生的频率，故选C； at the same time意为in the meanwhile同时；然而能够识别抗原的细胞是 ①吞噬细胞  ②T细胞  ③B细胞  ④记忆细胞  ⑤效应B细胞  ⑥效应T细胞 A.①②③④⑤⑥       B.②③④⑤⑥   C.①②③④⑥    D.①②③④