10. A rectangular floor measuring 17 feet by 10 feet is covered with 170 square tiles, each $1 \times 1$ square foot. A bug crawls from one corner to the opposite corner. Starting from the first tile it leaves, how many tiles does it cross in total?
(A) 17
(B) 25
(C) 26
(D) 27
(E) 28
10. C.

Assuming the insect crawls from the bottom left corner to the top right corner, it needs to pass through 16 horizontal lines and 9 vertical lines, plus the starting point, making a total of $16+9+1=26$ points, with each point corresponding to one tile.
Therefore, it has crawled over 26 tiles.