For this case we have that by definition, a flat angle is the space between an intersection between two lines whose opening measures 180 degrees.
Then, if we look at the figure we have to:

Thus, the angle ABC is
, less than 90 degrees, so it is an acute angle.
The CBD angle is
8, greater than 90 degrees, so it is an obtuse angle.
ANswer:

ABC is acute angle
CBD is obtuse angle