​Firms that have high cost of monitoring,choose their employees much more carefully because

A) ​They are afraid that the employee would be too productive
B) They are  more confident that after getting the job,the employee would not shirk
C) They are afraid that without screening,the employee would be more likely to shirk
D) ​B & C

As the number of securities in a portfolio is increased, what happens to the average portfolio standard deviation?

A) It increases at an increasing rate.
B) It increases at a decreasing rate.
C) It decreases at an increasing rate.
D) It decreases at a decreasing rate.
E) It first decreases, then starts to increase as more securities are added.