Answer:
A. Delete checked
Step-by-step explanation:
"Checked" in this sentence is redundant and unnecessary, as it makes this a run-on sentence.
Run-on sentence: There is a run-on sentence when two or more independent clauses are inappropriately joined.
This statement must be modified by deleting the word "checked" for good flow; alternatively, it might be rewritten using the following example:
- William searched behind the door, in the closet, and under the bed, but was unable to locate his second sneaker.