Which character trait of Sherlock Holmes does this excerpt from “The Adventure of the Speckled Band” by Sir Arthur Conan Doyle illustrate?

The lady gave a violent start and stared in bewilderment at my companion.

“There is no mystery, my dear madam,” said [Sherlock Holmes], smiling. “The left arm of your jacket is spattered with mud in no less than seven places. The marks are perfectly fresh. There is no vehicle save a dog-cart which throws up mud in that way, and then only when you sit on the left-hand side of the driver.”

“Whatever your reasons may be, you are perfectly correct,” said she. "I started from home before six, reached Leatherhead at twenty past, and came in by the first train to Waterloo.”

A.
his ambitious nature
B.
his perfectionist nature
C.
his tendency to be cautious
D.
his powers of observation