题目

. He was feeling bad. He went to work, _______, and tried to fix his attention on it.     A. however     B. so      C. although     D. while 答案：A小孔成像是由于___形成的,像是___(填“正立”或“倒立”)的。在其他条件不变的情况下,将物体远离小孔,像将___.(填“变大”“变小”或“不变”)