四边形ABCD中，AB=3、BC=4、CD=13、DA=12、∠CBA=90°，那么它的面积为（ ）
A．32
B．36
C．39
D．42
如图所示：连接AC，
∵AB=3，BC=4，∠CBA=90°，
∴AC=
=AB2+BC2
=5，32+42
∵△ACD中，52+122=132，即AC2+AD2=AC2，
∴△ACD是直角三角形，
∴S四边形ABCD=
S△ABC+S△ACD=1 2
×3×4+1 2
×5×12=36．1 2
故选B．
阅读下面短文，掌握其大意，然后从各题所给的四个选项（A、B、C和D）中，选出最佳选项。 There are many kinds of friends. Some are always ___1___you, but don't understand you. Some say only a few words to you, but understand you. Many people will step in your life, but only ___2___friends leave footprints (脚印). I shall always recall (回忆) the autumn and the girl with the ___3___ . She will always bring back the friendship between us. I know she will always be my best friend. It was the golden season. I could see the yellow leaves ___4___ on the cool ___5___. In such a season, I liked walking alone in the leaves, ____6__ to the sound of them. Autumn is a __7____ season and life is uninteresting. The free days always get me ___8___ . But one day, the sound of a violin __9____into my ears like a stream (小溪) flowing in the mountains. I was so surprised that I jumped to see what it was. A young girl, standing in the wind, was__10____ in playing her violin. I had __11____ seen her before. The music was so nice that I listened quietly. Lost in the music, I didn't know that I had been ___12___ there for so long but my existence (存在) did not seem to disturb her. Leaves were still falling. Every day she played the violin in the corner of the building ___13___ I went downstairs to watch her performance. I was the only listener. The autumn seemed no longer lonely and life became ___14___. __15____ we didn't know each other, I thought we were already good friends. I believe she also loved me. Autumn was nearly over. One day, when I was listening carefully, the sound suddenly ___16___. To my astonishment (惊讶), the girl came over to me. “You must like violin.” she said. “Yes. And you play very well. Why did you stop?” I asked. Suddenly, a __17____ expression appeared on her face and I could feel something unusual. “I came here to see my grandmother, but now I must leave. I once played very badly. It was your listening every day that _18_____ me.” she said. “In fact, it was your playing _19_____ gave me a meaningful autumn,” I answered, “Let's be friends.” The girl smiled, and so did I. I never heard her play again in my life. I no longer went downstairs to listen like before. Only thick leaves were left behind. But I will always remember the fine figure (身影) of the girl. She is like a __20____—so short, so bright, like a shooting star giving off so much light that it makes the autumn beautiful. 小题1:.
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