Answer:
Running takes discipline, and many people enjoy running.
Step-by-step explanation:
By combining independent clauses in a sentence, the writer reveals the relationships between the thoughts expressed by the clauses.
The conjunction and in the last option is an example of faulty coordination because you can hadly expect people to enjoy something that requires discipline. Discipline and enjoyment are hardly compatible for most people.
If we replace the conjunction and with the conjunction yet, we will show the correct relationship between the thoughts expressed by the clauses:
Running takes discipline, yet many people enjoy running.