If a tax is imposed on a market, under what conditions will sellers pay a bigger share of the tax than buyers?

a. When supply is more elastic than demand.

b. When the tax is a corporate tax.

c. When demand is more elastic than supply.

d. When the government imposes the tax directly on the sellers, so it is they who have to pay, rather than the buyers.

I put A for my answer and it was incorrect, what is the right answer and why?