题干

下列关于细胞的分化、衰老、凋亡的叙述,正确的是(  )

A:在细胞衰老和凋亡的过程中,细胞核的体积不断变小

B:细胞分化的过程中遗传物质不发生改变,但mRNA的种类和数量会改变

C:高度分化的细胞不具有分裂能力,故细胞核中的DNA不存在解旋的现象

D:细胞生长过程中体积增大,与外界环境进行物质交换的速率增强

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B

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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.