某植物块根的颜色由两对自由组合的基因共同决定．只要基因R存在，块根必为红色，rrYY或rrYy为黄色，rryy为白色；在基因M存在时果实为复果型，mm为单果型．现要获得白色块根、单果型的三倍体种子．

请写出以二倍体黄色块根、复果型（rrYyMm）植株为原始材料，用杂交育种的方法得到白色块根、单果型三倍体种子的主要步骤．____．

一辆运铺路砂石的汽车，车厢长2.4米，宽1.6米，高1米，把这样满满一车砂石铺到宽8米的路面上，如果要铺10厘米厚，可以铺____米？

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    A little mouse thought he was the tallest and strongest animal in the world. His mother said to him, "Don't say that in front of an elephant. He doesn't like that." The little mouse didn't listen to his mother. He went out to look for the elephant, but he didn't know who the elephant was. He asked an ant(蚂蚁) first, "Are you an elephant?" "No, I'm not," said the ant. "An elephant is much bigger than I am." Suddenly(突然), he saw four big trees. "Let me climb up(爬上) a tree. Then I can see where the elephant is," said the little mouse. "Get down! Get down!" someone shouted(喊) to him. "I'm the elephant. Go and climb that tall tree nearby. Then you can see me." "Now, I see. The elephant is the tallest and strongest animal in the world," said the little mouse.

******在十九届中共中央政治局常委同中外记者见面会上强调：我们将继续清除一切侵蚀党的健康肌体的病毒，大力营造风清气正的政治生态，以全党的强大正能量在全社会凝聚起推动中国发展进步的磅礴力量。这表明（    ）

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唐朝堪称我国古代文明开放社会的典范，唐朝时期政治清明、经济繁荣、文化昌盛、对外交往频繁，对后世影响深远。据此回答下列问题：