What Is the Main Limitation of Randomized Block Designs

Multiple Choice

What is the main limitation of randomized block designs?

A) They require an equal number of rows,columns,and treatment levels,which is sometimes problematic.
B) They do not allow the researcher to examine interactions of the external variables with each other or with the independent variable.
C) The researcher can control for only one external variable.
D) The number of treatment combinations increases multiplicatively with an increase in the number of variables or levels.