(multiple choice) A student is building a model roller coaster. The car rolls down from a standing start at the top of the first hill, which is 2 m high. The car fails to make it up to the top of the second hill, which is 2.1 m high. Ignoring friction and air resistance, which is MOST LIKELY the source of the problem?
A. The car has too much mass.
B. The second hill is higher than the first.
C. The car is going too fast at the bottom of the first hill.
D. The first hill is too high.