### Video Transcript

Which of the following is an
acute angle?

In this question, we need to
identify which of the five given angles is an acute angle. We can do this by recalling
that we say that an angle 𝐴𝐵𝐶 is acute if its measure is between zero and 90
degrees. We can see that of the five
given options, only option (D) has a measure between these values. Thus, it is the only acute
angle. We can also classify the other
angles using their measures. First, we recall that angles
with measure between 90 and 180 degrees are obtuse angles. So option (B) is an obtuse
angle, since its measure is 120 degrees.

Next, we recall that an angle
of measure greater than 180 degrees is a reflex angle. So option (A) is a reflex
angle. We can also recall that an
angle of measure 90 degrees is referred to as a right angle and that an angle of
measure 180 degrees is called a straight angle.

It is also worth noting that we
can answer this question without knowing the exact measures by noting that acute
angles must have smaller measure than a right angle. So we can compare the size of
the rotations to a quarter turn to see that only option (D) is an acute
angle.