被动语态

A。be seen to do被看到做某事。B结构不对。C是主动。D现在进行时不对。
关于B项：能跟不带to 的不定式作补足语的动词有：see,feel,hear,listen to,look at,watch,let,have,make,observe,notice。如：I saw him play in the street just now.而当这些词为被动式时，不定式要带to,如：He was seen to play in the street just now.

A,was seen to

be seen to do
被看到做了某事（全过程）

be seen doing
被看到正在做某事

选A，但是不是很好，因为just now最好是看到正在做的

但选A不会发生语法错误

选A
A。be seen to do被看到做某事。
B结构不对，能跟不带to 的不定式作补足语的动词有：see,feel,hear,listen to,look at,watch,let,have,make,observe,notice。如：I saw him play in the street just now.而当这些词为被动式时，不定式要带to,如：He was seen to play in the street just now.
C是主动。
D现在进行时不对。