Final answer:
The sentence requires a conjunction to correctly join the two independent clauses. The use of a conjunction like 'so' will connect the clauses, reflecting a cause and effect relationship between Will needing directions and buying a map. The correct option is (a) a conjunction.
Step-by-step explanation:
The sentence provided by the student contains two independent clauses: "Will needed directions" and "he bought a map." In English grammar, when two independent clauses are present, they must be joined using either a semicolon, a conjunction, or by making one a dependent clause. Since the diagram indicates a connection between "needed" and "bought" with dotted lines, the student is being guided to use a conjunction to connect these two independent clauses to form a compound sentence. Therefore, a conjunction is needed to correctly join these clauses. One possible correct version of the sentence would be: "Will needed directions, so he bought a map." This example uses the coordinating conjunction 'so', which is one of the coordinating conjunctions that can be used to join independent clauses, as mentioned in Chapter 12, Lesson 1.
It is crucial in constructing compound sentences to know how to use transitional words and phrases correctly, as they enhance the flow and clarity of the writing. For instance, the word 'so' in this context shows a cause and effect relationship between Will's need for directions and his purchase of a map. Any of the seven coordinating conjunctions (for, and, nor, but, or, yet, so) could be utilized, depending on the intended meaning of the sentence.
In summary, based on the incorrect sentence and its diagram, what must be added to the sentence is a conjunction to join the two independent clauses and form a coherent compound sentence. The correct option to add to the sentence is (a) a conjunction.