Hello LUANDATO.

Let's take a look at your question.

The volume of a cylinder container is $$V=\pi\cdot r^2\cdot h .$$ Now, we know that after 10 minutes it has been leaked out $$0.31\cdot10=3.1\ m^3\ of\ water.$$ On the other hand the water has decreased 0.25 meter. We now can build a cylinder of volumen 3.1m^3 and height 0.25. Then $$3.1=\pi\cdot r^2\cdot0.25\ \Leftrightarrow\ \ r^2=3.947\ \Leftrightarrow\ r=1.98.$$ This is why the correct answer is the option D.

I hope this answer can help you.

I'm availbale if you'd like a follow-up.

Regards.