Which of the following increases basis risk?

Question $7$ options:

a$)$

A reduction in the time between the date when the futures contract is closed and its delivery month

b$)$

A large difference between the futures prices when the hedge is put in place and when it is closed out

c$)$

None of the options

d$)$

Dissimilarity between the underlying asset of the futures contract and the hedger's asset exposure