be reluctant to

[keannu]

Why is a the only answer? Can't b be an answer as well? What is the difference between a and b?

A: The book club members want me to host our meetings at my house.
B: If I were you, I'd ___a___
a.be reluctant to
b.be reluctant to do
c.be reluctant to be
d.be reluctant to be doing

 

[5jj]

b would need 'that' following it.

 

[keannu]

b would need 'that' following it.

Is it because the sentence should be replacent like "I'd be reluctant to" or complete like "I'd be reluctant to host it", but "I'd be reluctant to do" is incomplete, so the meaning is unclear?