第二节根据所给句子意思以及汉语或首字母提示，写出下列各句中所缺单词的正确形式。(共15小题；每小题1分，满分15分)
11. If you _______________(违反) the regulations, you shall be fired. Be responsible for your job.
12. His father always reminded him to look out for ________________（潜在的）dangers ahead.
13. Leaving the doors unlocked is a(n) ________________ (诱因) to burglars.
14. At the end of each term, teachers are required to __________（评估）the performance of students.
15. I believe Mary will turn up at eight. I know she is always very ______________ (准时的）for meetings.
16. We shouldn’t change lanes without _________________(发信号) or giving wrong signals.
17. We cannot put the theory into practice because of the fact that it has been based on a series of wrong _________________. (假设)
18. His father a__________________（陪伴）him to school every day; he is too young to go alone.
19. Ann likes to buy goods in large q__________________ so that she needn’t go shopping often.
20. A sore throat and fever were the s__________________ of serious flu.
21. She has mastered English grammar and a__________________ a large vocabulary without the help of a teacher.
22. We had to p________________ going to France because the children were ill.
23. The young fellow is a__________________ and likely to quarrel with anyone at any time.
24. Time p_________________, I would like to go fishing with you this weekend.
25. On hearing the terrible accident, you could never imagine how I worried when I was told that you two went home s________________ on such a rainy night.
单链的比例
为 。某样品DNA分子中共含3000个碱基对，碱基数量满足：（A+T）/（G+C）＝1/2，若经5次循环，获得32个与样品相同的DNA分子，至少需要向试管中加入 个腺嘌呤脱氧核苷酸。（不考虑引物所对应的片段）
且与圆
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