visited the Shanghai World Expo is sure to tell you the place is worth visiting twice.A. T

问题补充：

visited the Shanghai World Expo is sure to tell you the place is worth visiting twice.

A. Those who have

B. Whoever has

C. Those who has

D. Whoever have

答案：

A. Those who have

(答案→)B. Whoever has

C. Those who has

D. Whoever have

解析：考查主谓一致：凡是已经参观了上海世博会一定会告诉你这个地方是值得去两次的。如果因为这句话的谓语是is，所以主语是单数，those做为主语的时候，谓语是复数，排除AC，而whoever引导主语从句，相当于anyone who，whoever引导的主语从句中的谓语也是单数，排除D，选B。