单选题 When a psychologist does a general experiment about the human mind. he selects people ______ and asks them questions.

【正确答案】 B
【答案解析】at random随意地;at length冗长地,详细地;in essence在本质上,实质上;in bulk整批地,大量地。句意:当一位心理学家要做关于人类思维的全面实验时,他就要随机选人并问他们问题。