Answer:
Option 1st.
Explanation:
Definition: 30-60-90 triangle
In 30-60-90 triangle,
the length of the hypotenuse is twice the length of the shorter leg, and
the length of the longer leg is
times the length of the shorter leg.
We have to find from the given triangles which triangle is a 30-60-90 triangle
Consider the length of shorter leg = 5 units
then by above definition we have;
Length of the hypotenuse = 2(5) = 10 units
and
Length of the longer leg =
units
Therefore, the only triangle which is a 30-60-90 triangle is, option 1st