If the adjacent sides of a parallelogram are equal then parallelogram is a
Rhombus
Step 1. Explanation for correct option
For option C
So, if the adjacent sides of a parallelogram are equal then parallelogram is a Rhombus.
So option C is correct.
Step 2. Explanation for incorrect option
For option A
In rectangle adjacent sides are not equal.
Opposite sides are equal .
So option A is incorrect
For option B
In trapezium is not a parallelogram.
So option B is incorrect
Hence, the correct option is (C).