Question

particles tend to speed up when what happens to them?
particle motion always stays the same.
they are heated.
they are cooled.

Explanation:

When particles are heated, the thermal energy increases. This added energy causes the particles to move more vigorously, resulting in an increase in their speed. Cooling particles has the opposite effect, reducing their motion. And it's incorrect to say particle motion always stays the same as external factors like heating or cooling can change it.

Answer:

They are heated.