I believe the first is B and the second C - right?
I also think the first one is B, because 2300 miles is the maximum distance the aircraft can travel before it reaches the point where it no longer has at least one hour of fuel available. So, it would need to land at an airfield less than 2300 miles away. A or B fit into this, but I think that we need to assume that the aircraft needs to travel as many miles as it can, thus A is out, I guess.
The second one is definitely not C. It's D. If the aircraft needs to descend from FL310 to FL280, then it needs to descend 3000 feet. If the descent rate is 1200 feet per minute, then it will descend 3000 feet in 2 and a half minutes (3000 / 1200 = 2.5), which is not one of the available answers.