Choose all the fractions that are in simplest form.
4/26
8/21
6/19
9/10
10/22

4/26 can be simplified by 2. So, this is not the answer.
8/21 cannot be simplified. So, it is one of the answers.
6/19 cannot be simplified. So, it is one of the answers.
9/10 cannot be simplified. So, it is one of the answers.
10/22 can be simplified by 2. So, this is not the answer.

So, the fractions in simplest forms are 8/21, 6/19, and 9/10.