$36 \cdot 32$ A student observed the weather for $x$ days during the summer vacation, and the results were:
(1) There were 7 sunny mornings;
(2) There were 5 sunny afternoons;
(3) It rained 8 times;
(4) On the days when it rained in the afternoon, the morning was sunny.
Then $x$ equals
(A) 8.
(B) 9.
(C) 10.
(D) 11.
(Chinese Jiangsu Province Junior High School Mathematics Competition, 1986)
［Solution］From (4), we know that there is no weather where it rains both in the morning and in the afternoon. Therefore, there can only be the following three scenarios:
Morning clear, Afternoon clear;
Morning clear, Afternoon rain;
Morning rain, Afternoon clear.
7 mornings clear, 5 afternoons clear
(a total of 8 rainy periods)

That is, a total of $7+5+8=20$ times or 20 half-day weather records.
Thus, $x=10$.
Therefore, the answer is (C).