θ∈R，则方程x²+$\frac{y^2}{\sin \theta }$=4表示的曲线不可能是（　　）

A Policeman and a Thief  
One day a policeman was taking a thief to the city . On the way , they saw a shop . The thief said . “ Let me go into the shop to buy some bread . We can eat it in the train . ”
The policeman agreed . The thief went into the shop and ran out of the back door . When the policeman knew that , he began to look for the thief everywhere . At last the policeman caught(抓获) thief again . They went on to the city . On the way they came to the same shop . The thief wanted to buy some bread again . “Oh , no . ” said the policeman , “You did that before , and you ran away . This time I^’ll go into the shop and buy bread . You must wait here for me . ”

两群孩子为争强而械斗，你的朋友吃了亏，受了气，让你帮助去还击出气，你的反映是（     ）