消化食物和吸收营养物质的主要场所是（    ）

    Tired of Working in Your Country?

With over 500 instructors and 20 years of experience, we are the leader in the field of teaching foreign languages. We now have positions open in Osaka starting September/October 2018 for instructions of English, German, Spanish and French.

    Teach many different kinds of classes using the latest technology in small classes of up to 30 students.

    Accommodation, and other necessary documents will be ready before you leave.

    Applicants will teach their first language only.

    Excellent teacher training programs.

    If you are young with a university degree and are willing to experience different cultures, apply now. Experience in teaching is an advantage but not specially required. Knowledge of the Japanese language is not necessary but good English skills and practical computer knowledge are basic requirements.

Apply with C.V. and send letter to:

    NOVA France, Mr. Sampy (IHT 3/2)

    34, Bd. Haussmann, 75009 Paris, France

    Fax: 33148014804

    Or visit our website: www. teachjp. com

    The manager expects to meet and talk with successful applicants in Paris in June and July.

下表是某实验小组同学做“研究滑动摩擦力的大小跟哪些因素有关”的实验记录：

如图所示，两平行金属导轨间的距离L=0.40m，金属导轨所在的平面与水平面夹角θ=37°，在导轨所在平面内，分布着磁感应强度B=0.50T、方向垂直于导轨所在平面的匀强磁场．金属导轨的一端接有电动势E=4.5V、内阻r=0.50Ω的直流电源．现把一个质量m=0.04kg的导体棒ab放在金属导轨上，导体棒恰好静止．导体棒与金属导轨垂直、且接触良好，导体棒与金属导轨接触的两点间的电阻R₀=2.5Ω，金属导轨的其它电阻不计，g取10m/s²．已知sin37°=0.60，cos37°=0.80，试求：