The correct answer is - b. staying low on the ground.
Whenever there's a thunderstorm, few things should be avoided in order to increase ones security and not get hit by an electrical charging from the sky.
Some of the things to be avoided are the higher trees, because the thunderstorms tend to hit the highest objects, and the water, because the water is excellent transmitter of electricity.
The best thing to do, is to get away from any water body, or high spot or tree, and be low on the ground, if possible lie on the ground, because in this case, the person will not be sticking out in the surrounding area, thus the chances of getting hit will be much smaller.
