九、课文原句填空（每空0.5分，共5分）

1. Polly found herself ______ _____ _____ a man standing with his hand _________ on her arm.

2. In 1066, the Normans conquered English and _______ ______ ______ the country.

3. Unfortunately, all the people were _______ _______, and _______ was the city.

电视机的显像管中，电子束的偏转是用磁偏转技术实现的。电子束经过电压为U的加速电场后，进入一圆形匀强磁场区，如图所示。磁场方向垂直于圆面。磁场区的中心为O，半径为r。当不加磁场时，电子束将通过O点而打到屏幕的中心M点。为了让电子束射到屏幕边缘P，需要加磁场，使电子束偏转一已知角度θ，此时磁场的磁感应强度B应为多少？