28. Helen has just got a new bike. It has a speedometer which sits on the handlebar. The speedometer can tell Helen the distance she travels and her average speed for a trip. 

 On one trip, Helen rode 4 km in the first 10 minutes and then 2 km in the next 5 minutes. Which one of the following statements is correct?
(A)Helen’s average speed was greater in the first 10 minutes than in the next 5 minutes.
(B)Helen’s average speed was the same in the first 10 minutes and in the next 5 minutes.
(C)Helen’s average speed was less in the first 10 minutes than in the next 5 minutes.
(D)Helen’s average speed was less in the first 10 minutes than in the next 5 minutes.