Suppose a cart is being moved by a force. if suddenly a load is dumped into the cart so that the carts mass doubles, what happens to the carts acceleration?

Gravity
will pull it down

If the heat engine is a perfect carnot cycle engine, thenefficiency = (t2-t1)/t2   where t1=temperature of cold reservoir ( ° k) = 135            t2=temperature of hot reservoir ( ° k)   = 325thereforeefficiency = (t2-t1)/t2 = (325-135)/325 = 0.5846 = 58%  note: this is the theoretical maximum efficiency of a perfect heat engine.   real-life engines do not achieve this value.

'b ' is the correct conclusion.