Select the most appropriate option to fill in the blank and make a grammatically correct sentence
The driver of the car probably holds the key to ______ the crime.

Options

A. i) solving
B. ii) solves
C. iii) solved
D. iv) solution

Explanation

solving In the given sentence, the key means a thing that makes you able to understand or achieve something. Here key should be followed by (to doing something) to “solving”.