There are three ways a sentence can be written-
1) Simple sentence- A simple sentence is made up of only one clause. It is made up of a subject, verb and a completed thought.
2) Compound Sentence- A compound sentence consists of two or main clauses which are joined using a coordinating conjunction ( for, and, nor, but, or, yet, so).
3) Complex Sentence - A complex sentence consists of one independent clause and one or more dependent clause. A dependent clause cannot stand alone as a sentence. Therefore, subordinating conjunctions are used before a dependent clause. Some of the most common subordinating conjunctions include after, although, as ,before,while, wherever, whereas,unless, until,though, when, since, even though,if, since, because.
The correct answers are C)Having a car enables you to travel round more easily. and D)Having a car enables you to travel round more easily..
Options C and D are correct as the given sentence is a complex sentence and to convert it into a simple sentence, the dependent clause is contracted to a word or phrase(Having a car enables you,To have a car enables you).
The other options are wrong as if and so cannot be used.