14) How many angles greater than $90^{\circ}$ can a quadrilateral (non-intersecting) have?

(A) It always has at least one

(B) it has at most one

(C) it has at most two

(D) it has at most three

(E) it can have four.
14) The answer is $(\mathbf{D})$.

Indeed, the sum of the angles is $360^{\circ}$, so at least one of them must be less than or equal to $90^{\circ}$. On the other hand, if one takes a triangle $A B C$ with angles at $A, B, C$ respectively equal to $25^{\circ}, 95^{\circ}, 60^{\circ}$ (for example) and it is flipped with respect to the side $A C$, a quadrilateral $A B C D$ is obtained that has three obtuse angles. To verify that answer (A) is also incorrect, consider the case of a rectangle.