1. If the perimeter of a triangle is even, and the lengths of two of its sides are 2 and 5, then the shape of this triangle must be ( ).
(A) right triangle
(B) isosceles triangle
(C) isosceles right triangle
(D) cannot be determined
-、1. B.
Let the third side be $c$. Then $3<c<7$. Also, $c$ must be an odd number, so $c=5$.