Answer: The argument is valid by the law of syllogism
Step-by-step explanation:
Given :-If a quadrilateral has opposite sides that are parallel, then it is a parallelogram.
A rhombus is a quadrilateral where the opposite sides are parallel.
then by law of syllogism (reasoning of transitivity) the conclusion is "A rhombus is a parallelogram."
Law of syllogism is similar to reasoning to transitivity i.e. if a=b and b=c then a=c.