Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

Most have cells that are not able to exchange gases with the outside environment do multicellular organisms need transport systems.
Why do multicellular organisms need transport systems?

The heterotroph eats only or mainly plants.
The heterotroph eats only or mainly what?

In the past, asteroids colliding with planet earth has caused many organisms to die off.
In the past, what colliding with planet earth has caused many organisms to die off?