单选题 How do WHO experts react to this special case in Vietnam?

A、 They have confirmed that the sisters in the case were infected from poultry.
B、 They link all the members in the family to contact with sick birds.
C、 They are quite doubtful of the possibility of human-to-human transmission.
D、 They feel astonished because it's the first time they found such a case.

【正确答案】 C

【答案解析】细节题。题目问的是：WHO专家对越南的这个特殊案例作何反应?文章第六段第一句话提到：The WHO spokesman in Vietnam says experts are considering the possibility of human-to-human transmission“WHO在越南的发言人声称专家们正在考虑人到人传播的可能性”。由此可以判断出[C严他们十分怀疑人到人传播的可能性”与文章的意思相符。