Our journeys into outer space brought us closer to understanding the universe. they also left behind numerous pieces of garbage known as “space junk” that pose threats to spacecrafts and space stations. this orbiting dump includes thousands of nuts, bolts, gloves, and other debris. data from a 1999 study indicate there around 110,000 objects larger than 1 centimeter orbiting the earth left from our ventures into space. even the smallest of these could do serious harm to a satellite or space-based telescope. it could also threaten the lives of those aboard the international space station. u. s. space command takes responsibility for keeping an eye on space junk. this agency reports any potential threat to nasa, which sometimes must order emergency maneuvers to avoid space collisions.

what does the author use to support the idea that space programs have left behind a lot of debris?

a. the author quotes scientists and other experts who give their views about space junk.
b. the author quotes statistics on how many pieces of space debris have struck spacecraft.
c. the author refers to a study that estimated the number of space junk objects.
d. the author uses personal experience to describe the extent of garbage in space.