To represent the situation where the total number of items in the candy shop is 100, we need to add the quantities of each type of item: chocolates, cookies, and truffles. We have 25 chocolates and 17 cookies, and we need to include the variable \( T \) for the number of truffles.
The correct equation representing this situation is:
\[ 100 = 25 + 17 + T \]
Therefore, the correct answer is:
C. \( 100 = 25 + 17 + T \)