Clue words showing that contrasts are being made in this paragraph include

A. Both and Difference.

B. And and Similar.

C. Also and Hand.

D. While and However.

D. While and However.

An example is,

John has a skateboard while his friend Jack doesn't.

The scientists found out that there is a correlation between happiness and belongingness however, there was the presence of a third variable.

There is the presence of conjunctions like because, as, since, hence, and etc.

Most likely like a compound sentence being connected by a conjunction. A compound sentence is formed "by joining two simple sentences with a comma and a coordinate conjunction". Some of the coordinate conjunctions that are used to connect these two simple sentences are and, but, so, or, for, nor, yet and many more. Below are some examples of compound sentences.