Presenting Students with Several Essay Questions and Permitting Them to Choose

Presenting students with several essay questions and permitting them to choose any two of them to respond to is an undesirable testing practice for which of the following reasons?

A) it encourages students to write more on each question
B) it is difficult for students to adequately prepare for the test
C) the basis of comparing students is undermined
D) students do not have an opportunity to demonstrate all that they have learned