Our primary concern over here is oil spill and not monetary benefit.
According to the author bringing oil in tanker is very risk, but If we can prove to the author there are methods to make this process risk free then we are proving him wrong and A does just that.

(A) Tankers can easily be redesigned so that their use entails less risk of an oil spill.: correct

But options D and E talk about damage to ocean flour and monetary benefit and both are irrelevant in the present context,

(D) Offshore operations usually damage the ocean floor, but tankers rarely cause such damage.
(E) Importing oil on tankers is currently less expensive than drilling for it offshore.

Other options ,

B supports author .
C is irrelevant.