Concept:Since at least one question must be chosen from each of the 3 sections, the 5 selected questions can be distributed among the sections only in these two patterns:
(1,1,3) or
(1,2,2), taken in all possible orders.
Explanation:There are 3 sections, each having 5 questions.
For the distribution
(1,1,3): the number of ways is
(15​)(15​)(35​)=5×5×10=250.
The section that gets 3 questions can be any of the 3 sections, giving
3×250=750 ways.
For the distribution
(1,2,2): the number of ways is
(15​)(25​)(25​)=5×10×10=500.
The section that gets 1 question can be any of the 3 sections, giving
3×500=1500 ways.
Therefore, total number of ways
=750+1500=2250.
Answer:2250, which is option D.