Which statement is correct?

Which statement is correct?

a$.$ A non$-$cash business benefit under s$21$A$,$ less than $$1000$ is exempt from tax.

b$.$ Exempt income may decrease a deduction for a tax loss.

c$.$ Only specific deductions are possible against exempt income.

d$.$ The disposal of an asset used to generate exempt income can be used to produce a capital gain or loss.