Triangle ABC is an obtuse triangle with the obtuse angle at vertex B. Angle A must be less than 90°.
greater than 90°.
congruent to angle B.
congruent to angle C

"less than 90°."

Step-by-step explanation:

This is because an obtuse triangle can be defined as "An obtuse triangle (or obtuse-angled triangle) is a triangle with one obtuse angle (greater than 90°) and two acute angles." Therefore, there can only be ONE obtuse angle. Therefore, with the obtuse angle being at vertex B, there cannot be another one at vertex A.

21

jk it's 20

step-by-step explanation: