When two variables interact (Multiple Choice)

When two variables interact
 
  a. the effect of one variable depends on the level of the other
  b. the main effect cannot be interpreted without discussing the interaction
  c. the effect of one variable does not depend on the level of the other
  d. both a and b

Question 2

There is an interaction if
 
  a. there is no main effect of either Variable A or Variable B
  b. the effect of Variable A depends on whether there is a main effect of Variable B
  c. there is a main effect of both Variable A and Variable B
  d. the effect of Variable A depends on the level of B