[单选题]关于流动式起重设备安全施工，正确的做法是( )。
A.在平整地基上吊装时支腿不应铺设垫木
B.吊装前支腿应全部打开
C.吊装前只需前支腿打开
D.吊装前只需后支腿打开

Washington Irving was the American first man of letters to be known internationally. His works were received enthusiastically both in England and in the United States. He was, in fact, one of the most successful writers of his time in either country, delighting a large general public and at the same time winning the admiration of fellow writers like Scott in Britain and Poe and Tarwthorne in the United States. The respect in which he was held was partly owing to the man himself, with his warm friendliness, his good sense, his politeness, his gay spirits, his artistic integrity, his love of both the old World and the New. Thackeray described Irving as a "gentleman, who, though himself born in no very high sphere, was most finished, polished, witty; socially the equal of the most refined Europeans". In England he was granted an honorary degree from Oxford -- an unusual honor for a citizen of a young, uncultured nation -- and received the medal of the Royal Society of Lite
A. His background helped him to make literary achievements.
B. He spent much time learning law.
C. Though a gifted child he was, he received poor education.
D. His religious belief helped him a lot.

许多时候，我们不是跌倒在自己的缺陷上，而是跌倒在自己的优势上，因为缺陷能给我们以提醒，而优势却常常使我们忘乎所以。正如唐代诗人杜荀鹤写的《泾溪》云：“泾溪石险人兢慎，终岁不闻倾覆人。却是平流无石处，时时闻说有沉沦。”
请分析说明材料是如何体现矛盾的基本属性的？用一个汉语成语描述一下材料对你的启示。