如图所示结构中两杆的材料相同,横截面面积分别为A和2A,则该结构的许用载荷是 ()。
A. [F]=A[σ]
B. [F]=2A[σ]
C. [F]=3A[σ]
D. [F]=4A[σ]
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According to the speaker, what was most likely held by children in family portraits?
A. Their playings.
B. Some money.
C. Their relatives' hands.
D. Their shoes.
股票X和股票Y,这两只股票下跌的概率分别为.4和0.5,两只股票至少有一只下跌的概率为0.7,那么,这两只股票同时下跌的概率为()。
A. 0.9
B. 0.7
C. 0.4
D. 0.2
According to the speaker, what do most people think historians are concerned with?
A. Portraits as clues to our past.
B. Prominent families in history.
C. Twentieth century photographers.
D. A new generation of artists.
Where did the woman learn about this problem?
A. From a lecture.
B. In a magazine article.
C. In a book.
D. On a television program.