Can you define one SI based unit?

Great example of why you should study course notes instead of Googling answers. Kilogram is technically an SI unit AND one of the 7 "basic" SI units. And if you are simply looking for a "did you read everything in the textbook" question, it would be correct.

But the intent of the question, in my opinion,is to differentiate between a base value and prefix values for unit conversions. Remember, this is a middle school/high school class. I prefer to teach students to learn the process skills rather than to memorize historical trivia. The question could be written better and should probably reference "metric" rather than SI, but the answer is Liter.