Which of the following could be the lengths of the sides of a  30°-60°-90°  triangle?

C. √3, 3, 2√3 is your answer

Note that 30°-60°-90° triangle has the measurements of 1, √3, 2.

In this case, we are multiplying √3 to all sides

1(√3) = √3
√3(√3) = 3
2(√3) = 2√3

C. √3, 3, 2√3 is your answer

hope this helps