下图利用“通电导体在磁场中受力运动”原理工作的是（   ）

Ms Jones needs one____(人)to help her do the work．

如图,正方体ABCD-A₁B₁C₁D₁中,点M是A₁D₁的中点,点N是CD的中点,用反证法证明直线BM与直线A₁N是两条异面直线.

根据短文理解，选择正确答案。
Captain Goodfellow
    Do your children enjoy interesting stories, funny games, and exciting dances? Captain Goodfellow will be ready to teach all these things to children of all ages at the City Theatre on Saturday morning at 10:00, FREE.
Walking Tour of the Town
    Forget your worries on Saturday morning. Take a beautiful walk and learn about local history. Meet at the front entrance of the City Hall at 9:30. Wear comfortable shoes!
Film at the Museum
    Two European films will be shown on Saturday afternoon at the Museum Theatre. See Broken Window at 1:30. The Workers will be at 3:45. For further information, call 4987898.
International Picnic
    Are you tired of eating the same food every day? Come to the Central Park on Saturday and enjoy food from all over the world. Delicious and not expensive. Noon to 5:00 pm.
Do You Want to Hear “The Zoo”
     “The Zoo”，a popular rock group from Australia, will give their first US concert tomorrow night at 8 at Rose Hall, City College.

面对人口、资源、环境方面的国情，我国必须实施的战略是（   ）