Which of the following is most useful to scientists in measuring the size of asteroids?
a) the speed at which the asteroid is traveling.
b) the location of the asteroid in the solar system.
c) the gravitational effect when spacecraft flies close to the asteroid.
d) the composition of the asteroid.

c-The gravitational effect when spacecraft flies close to the asteriod

Explanation:

Gravitational effect on the spacecraft gives an estimate that how big is the asteroid by experiencing its gravitational pull.

The amount of extra thrust required to maintain the trajectory of the spacecraft during its motion hints at the scientist about the size of the asteroid.

Gravitational pull is directly proportional to the mass of object so greater the mass, greater will be the pull.

explanation:

the masses of the objects and the distance between them

the duration of a photographic flash is related to an rc time constant, which is 0.100 μs for a certain camera.