Read the excerpt from The Secret Garden:

The most absorbing thing, however, was the preparations to be made before Colin
could be transported with sufficient secrecy to the garden... It was almost as serious and elaborately thought out as the plans of march made by great generals in time of war.

What is the meaning of the figurative language "the plans of march made by great generals in time of war"?

A) They need a lot of people to help them.
B) It is a big undertaking.
C) It took a great deal of strategic preparation.
D) They must be careful and go undetected.