The answer is C: A teacher assigns a 10 page research project and says, "this might take a little time".
An understatement is a statement that underplays the significance, value, size, relevance or importance of something and it makes it seem considerable less than what it actually is. In this example, the teacher makes it seem like writing a 10 page essay will take just “a little time”, when in fact, any student knows that a 10 page essay in a considerable enterprise that will take a lot more than just a little time.