Most asteroids are discovered

a. during spacecraft flybys.

b. when they impact earth.

c. when they leave a trail in long-exposure photographs.

d. when they rapidly streak across the sky.

B. when they impact Earth.

Explanation:

Asteroids are minor planet type rocky masses that are broken off and found in the inner solar system and also been called the inner planetoids as they are orbiting around the sun. They are similar to comets based on surface features. Computerized methods are used to find out the presence of asteroids in the shy. The asteroid belt has tended to evolve in the nebula formation of the sun with the presence of heavy metals sinking in the ice cores leaving the rocky mineral in the crust. They are almost 1000 km to 1 meter wide and can be large as miniature planets  However waste the majority of them are irregular in the shade the three largest asteroids are Ceres, Vesta, and Pallas that form a type of the dwarf planet.

Answermost of the time it would be ground into fine sediment,and sometimes they are carried away from the original location;

Ca mega city if i’m not mistaken