There is a triangular park with vertices at $O$, $A$, $B$. At vertex $O$ there is an observation tower 150 meters high. A person standing on the observation tower observes the other two vertices $A$, $B$ on the ground and the midpoint $C$ of $\overline{AB}$, measuring angles of depression of $30^{\circ}$, $60^{\circ}$, $45^{\circ}$ respectively. The area of this triangular park is （15）（16）（17）（18）$\sqrt{(19)}$ square meters. (Express as a simplified radical)

On a plane, there is a trapezoid $A B C D$ with upper base $\overline { A B } = 10$, lower base $\overline { C D } = 15$, and leg length $\overline { A D } = \overline { B C } + 1$. Select the correct options.
(1) $\angle A > \angle B$
(2) $\angle B + \angle D < 180 ^ { \circ }$
(3) $\overrightarrow { B A } \cdot \overrightarrow { B C } < 0$
(4) The length of $\overline { B C }$ could be 2
(5) $\overrightarrow { C B } \cdot \overrightarrow { C D } < 30$

ABCD is a parallelogram AECD is a trapezoid $| \mathrm { BE } | = 3 \mathrm {~cm}$ $| \mathrm { DC } | = 4 \mathrm {~cm}$
If the area of the parallelogram ABCD in the figure is $20 \mathrm {~cm} ^ { 2 }$, what is the area of triangle $CBE$ in $\mathbf { cm } ^ { \mathbf { 2 } }$?
A) 7
B) 7,5
C) 8
D) 8,5
E) 9