23. Tom has 12 cards labeled with numbers, and he places these cards into boxes labeled $A, B, C, D, E$, such that the sum of the numbers in each box is an integer, and the sums of the numbers in the boxes from $A$ to $E$ are consecutive and increasing. It is known that the 12 cards are labeled with the numbers $2, 2, 2, 2.5, 2.5, 3, 3, 3, 3, 3.5, 4, 4$. 5. If a card labeled 2 is placed in box $E$, and a card labeled 3 is placed in box $B$, then the card labeled 3.5 must be placed in ( ) box.
(A) $A$
(B) $B$
( $\mathrm{C}) C$
(D) $D$
(E) $E$
23. D.

Notice that, the sum of the 12 card numbers is 35, with an average value of 7.

From the given information, the sum of the numbers in these five boxes is sequentially 5, 6, 7, 8, 9.

And $2 \cdot 5+3 \cdot 5=6, 2 \cdot 5+4 \cdot 5=7, 3.5+4.5=8$, and box $B$ already contains the number 3, box $E$ already contains the number 2, so the number 3.5 can only be placed in box $D$.