推动物理课本在小桌面上做匀速直线运动，物理课本共受____ 个力的作用，其中除推力和受到的摩擦力是一对平衡力之外，还有受到的____ 力和____ 力是一对平衡力．

    Mrs．Marks bought a printer yesterday．She was h____ because she could print anything she wanted at any time．H____,after about an hour, she was angry because she couldn't print the color blue．All the other c____ printed free, except(除了)blue，which was very unusual．

    She d____ to call the after-sales service department(售后服务部)to help her solve the problem．David answered the phone．He t____ everything he could think of to help Mrs．Marks．He asked her to reinstall(重新安装) the program，to reboot (重新启动)the computer and to turn the printer on and off．N____ of these things helped．

After hours of trying，the problem s____wasn't solved．Finally, David asked Mrs．Marks if he could go to her h____and try to solve the problem in  person．Mrs．Marks agreed and t____ him her address(住址)．When he arrived at her house，she showed him her computer and the printer. David u____what the problem was right away．He told her,“From now on，print on white paper instead of blue!”

—Thank you, Jane.I will.