【正确答案】 B

【答案解析】[解析] puzzle：谜。mystery：谜。His death has remained a puzzle. 他怎么死的至今还是个谜。It was a mystery how the burglars got in. 盗贼怎么进来的是个谜。problem：问题。We have lots of problems to solve. 我们有许多问题要解决。question：问题。The clever student asked the teacher an extremely difficult question. 那个聪明的学生问了老师一个极其难的问题。point：论点。The point that l want to make here and now is that Ph.D. dissertations must be original. 此时此地我想要说的一点是博士论文必须具有原创性。