"Which of the following statements is true?
a. If ∠1 has a measure of 90°, then ∠1 is obtuse.
b. If ∠1 has a measure of 140°, then ∠1 is acute.
c. If ∠1 has a measure of 35°, then ∠1 is acute.
d. If ∠1 has a measure of 180°,then ∠1 is right.