对于数据表：student(sno,sname,sex,age,grade)，查询学习成绩为空的学生的学号和姓名，下面语句正确的是______。

A．SELECT sno,sname FROM student WHERE grade=NULL

B．SELECT sno,sname FROM student WHERE grade IS NULL

C．SELECT sno,age FROM student WHERE grade IS NULL

D．SELECT sno,age FROM student WHERE grade=NULL

Which of the following is most likely to result in a capital market line (CML) that is not a straight line（）

A. Investors’ risk tolerance decreasing.

B. Borrowing rate exceeds the lending rate.

C. Increase in the proportion of the portfolio invested in the risk-free asset.