which was not a difficult thing

English as a Second Language English Vocabulary, Grammar and Idioms
1

Can one say:

[color=red]a. He had to take the old man home and give him dinner, which was not difficult to do.
b. He had to take the old man home and give him dinner, which were not difficult to do.

c. He had to take the old man home and give him dinner, which was not a difficult thing to do.
d. He had to take the old man home and give him dinner, which were not difficult things to do.

Many Thanks.

2

(a) © and (d) are all fine but (b) is wrong because ‘which’ refers in that sentence to the whole sentence and not the individual actions in it and has to be followed by the singular verb (was).