(1) The mechanic performed a number of diagnostic tests on the car.
(2) The mechanic used a computer to perform the diagnostic tests.
What is the BEST way to combine sentence 1 and sentence 2?
This choice makes it clear that the mechanic used the computer in order to perform the tests. Choice A makes the use of the computer appear incidental, while Choice C suggests that the mechanic was obliged to perform the tests because he used a computer.