do you have any work to do?if any,i'll be of ——————

do you have any work to do?if any,i'll be of ——————
do you have any work to do?if any,i'll be of ______
A：helpful
B：greatful
C：help
D：helpless
AB直接可以排除,我查了一下D选项的意思,词性是形容词好像也可以排除掉,但是句意选C不对诶,