3. (3 points) There are four points on a plane, and no three points lie on a straight line. Connecting these four points with six line segments, the number of triangles that can be formed using these segments as sides is ( ).
A. 3
B. 4
C. 6
D. 8
【Analysis】According to the definition of a triangle (a figure formed by three line segments that are not on the same straight line, connected end to end in sequence is called a triangle) fill in the blank.

【Solution】Solution: As shown in the figure below: Assume there are four points $A, B, C, D$ on a plane, where no three points are on the same straight line,

Therefore, the triangles that can be formed using these points as vertices are: $\triangle A B C, \triangle A B D, \triangle A C D$, and $\triangle B C D$, a total of 4. Hence, the answer is: $B$.