题干

关于摩擦力,下列说法正确的是(  )

A:物体受到摩擦力作用时,一定受到弹力作用

B:只有运动的物体才有可能受滑动摩擦力作用

C:具有相对运动的两物体间一定存在摩擦力作用

D:摩擦力的方向一定与物体运动方向相反

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A

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Best Travel Guides by Continent

     We've broken down(分类)the best travel guides, by continent, to help you find student discounts and travel like a local on your next adventure.

Europe—Let's Go Europe 2017: The Student Travel Guide

     Let's Go was founded about 55 years ago when a Harvard student had an idea to provide accessible, budget travel lips for young people. Students lave its amusing pages. Let's Go Europe 2017 has everything you need for your trip—from the best beer in Brussels to how to avoid the lines at the Louvre.

Africa—The Rough Guide to Cape Toxin, the Winelands, and the Garden Route

     With its colorful photos and detailed tips on how to make the most of South Africa, The Rough Guide is the book to gel when visiting Africa. You may not have access to Google Maps when you1 re out exploring but that's OK. The Rough Guide also comes with easy use to maps.

     It can be purchased as an eBook, or as a paperback(平装本).

Asia—Lonely Planet: South-East Asia on a Shoestring

     This guide is perfect for those backpacking through the hidden treasures of South-Ea.sl Asia. With detailed recommendations from experts in the area, this guide helps first-timers as well as experienced backpackers. This book can lie purchased as a paperback travel guide. A download for an eBook or separate chapters can be purchased to serve as a guide to specific cities.

North America—Planet USA Travel Guide

     With detailed reviews of the best places to eat, sleep, and explore, Lonely Planet is linked with budget-friendly attractions and that's why it makes our best travel guides list. This travel guide is available in paperback.