Question

which is a run - on sentence? air and water pollution are serious worldwide problems, engineers designed the car, it runs on electricity.

Explanation:

A run - on sentence combines two or more independent clauses without proper punctuation or a coordinating conjunction. The second sentence "Engineers designed the car, it runs on electricity." has two independent clauses ("Engineers designed the car" and "it runs on electricity") joined only by a comma, which is a comma - splice, a type of run - on. The first sentence is a complete and correctly punctuated sentence.

Answer:

Engineers designed the car, it runs on electricity.