【单选题】Topic sentence________________________________. One very real problem is that of traffic signs and signals. Those that are red green colour blind have trouble seeing stop signs found on shady streets ...
A.
Colour-blind people do not have so many problems as we expect.
B.
Colour-blind people have problems that we do not understand at all.
C.
Colour-blind people have problems that people who perceive colour never think about.
D.
Colour-blind people have problems that will be solved in the near future.