Answer:
a.
The triangle ABC is congruent to the triangle DFE by the SSS congruence rule.

b.
The triangle UVW is not necessarily congruent to the triangle YZX because it has only two corresponding congruent sides.
c.
The triangle MNO is congruent to the triangle PRQ by the SAS congruence rule.

Step-by-step explanation:
Given the figures in the attached image;
a.
The triangle ABC is congruent to the triangle DFE by the SSS congruence rule.

Note that all the three corresponding sides are congruent.
b.
The triangle UVW is not necessarily congruent to the triangle YZX because it has only two corresponding congruent sides.
c.
The triangle MNO is congruent to the triangle PRQ by the SAS congruence rule.

Note that it has two pairs of congruent sides and a pair of congruent angles.