When a psychologist does a general experiment about the human mi

When a psychologist does a general experiment about the human mind, he selects people （）and ask them questions.
A、at length
B、at random
C、in essence
D、in bulk
【正确答案】：B
【题目解析】：at length最后，详细地；at random随机地；in essence本质上，大体上；in bulk大批地。因此选B