1. The students of Class (1), Grade 3 in a certain school plan to go mountain climbing on Sunday. They plan to set off at 8:30 am, and try to climb the farthest mountain on the map. After reaching the summit, they will hold a 1.5-hour cultural and entertainment activity, and must return to the base before 3 pm. If the average speed on the way there is 3.2 km/h, and the average speed on the way back is 4.5 km/h, the farthest summit they can reach is ( ).
(A) $A$
(B) $B$
(C) $C$
(D) $D$
$-、 1 . D$.
Assuming the distance from the starting point to the top of the mountain is $x$ kilometers, then $\frac{x}{3.2}+\frac{x}{4.5}+1.5 \leqslant 6.5$.
Solving for $x$ gives $x \leqslant 9.3$.