Once a difficult and even dangerous place , Vietnam is now a friendly detestation that weles visitors from all over the world .
A. considered; visiting
B. considered; to visit
C. considering; visiting
D. considering; to visit
网友回答
A. considered; visiting
(答案→)B. considered; to visit
C. considering; visiting
D. considering; to visit
解析：考查状语从句的省略句和不定式：句意：虽然曾被认为不适宜旅游甚至危险，现在越南已是全世界游客的目的地。当主从句的主语一致的时候，可以省略从句的主语和be动词，这句话完整的是Once vienam is considered a difficult and even dangerous place,可以省略主语和be动词，所以填considered，第二空是词组wele sb to do sth欢迎某人做…，选B。