下列各项不是遗传物质变化引起的变异的是（      ）

某同学先后对同一面鼓轻敲和重击一下，两次发出声音的（　　）

    Friendship is the most important thing in the world. But how do you find a real friendship and keep it?

    An American writer tells young students some smart ways to find friends. He says finding friendship is just like planting a tree. You plant the seed(种子) and take care of(照顾) it to make it grow(生长).

    First, to make friends, you must be kind and friendly to others. You should learn to smile at others and try to make a stranger(陌生人) feel at home. You should think more of others than of yourself.

    Second, friends should negotiate(商量). When you don't agree with someone, please discuss with him or her. But even the best friends can fight. After the fight, you have to talk to him or her. If he or she doesn't want to talk, you could write a letter. Tell him or her how you are feeling, and tell him or her why you did this or that.

    Finally, if he or she leaves you when you are in trouble, never believe in him or her. And never leave your friend when he or she is in trouble. Remember, a friend in need is a friend indeed.

材料一：随着新航路的开辟和商业资本主义殖民高潮，整体世界资本市场开始形成；从资本主义萌芽到手工工场，从蒸汽时代到电气时代，从电气时代到信息时代，都对经济全球化起到了巨大的推动作用。——摘自百度文库《资本主义发展与经济全球化》

材料二：历史地看，经济全球化是社会生产力发展的客观要求和科技进步的必然结果，不是哪些人、哪些国家人为造出来的。经济全球化为世界经济增长提供了强劲动力，促进了商品和资本流动、科技和文明进步、各国人民交往。

    当然，我们也要承认，经济全球化是一把“双刃剑”。当世界经济处于下行期的时候，全球经济“蛋糕”不容易做大，甚至变小了，增长和分配、资本和劳动、效率和公平的矛盾就会更加突出，发达国家和发展中国家都会感受到压力和冲击。反全球化的呼声，反映了经济全球化进程的不足，值得我们重视和深思。——***《2017达沃斯论坛演讲》