Which of the Following Is a Justification for Overidentification Tests

Multiple Choice

Which of the following is a justification for overidentification tests?

A) If each instrument satisfies both the inclusion and exclusion condition, than using each instrument alone should produce an unbiased estimate of B1.
B) If each instrument satisfies both the inclusion and exclusion condition, than using each instrument alone will produce biased results.
C) Once we identify the excessive identification condition, the efficiency of our estimates will improve.
D) They allow us to identify weak instruments.