Question

which challenges do countries face in limiting the spread of communicable diseases?
lack of available healthy food
increase of worldwide travel
decrease of available clean water
increase in migration of infected animals

Explanation:

全球范围内旅行增加会使感染者更易流动，从而加大传染病传播限制难度。其他选项虽也影响健康，但与传染病传播限制的直接关联较小。

Answer:

B. increase of worldwide travel