When and where to go for on-salary holiday ______yet.

1.a
2.c
3.a

D.has not been decided
有When and where 开头须用单数

由and/both...and连接的并列主语的主谓一致问题
由and/both...and连接的并列结构作主语,可根据主语的意义决定谓语动词的单、复数形式.
例如：
Pancakes and syrup is a tasty breakfast.
The number and diversity of British newspaper is considerable.
Good and bad taste are inculcated by example.
Fish and chips are getting very expensive.
A truck and a car were in the ditch.
Both Cathy and her daughter Lida have gone fishing in Canada.
当and连接的并列名词词组带有each,every,或者many a 等限定词时,谓语动词通常用单数.
例如：
Each man and each woman there is asked to help.
Every flower and every bush is to be cut down.
Every change of season,every change of weather,indeed every hour of the day,produces some change in the magical hues and shapes of these mountains.
Many a boy was disappointed after seeing the film.你自己好好看看吧.