题目内容

蜗杆传动用于传递空间交错两轴间的运动和转矩，通常两轴间的交错角等于（）

A. 180度
B. 90度
C. 45度
D. 30度

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You want to display the titles of books that meet these criteria: 1. Purchased before January 21, 2001 2. Price is less then $500 or greater than $900 You want to sort the results by their data of purchase, starting with the most recently bought book. Which statement should you use? （）

A. SELECT book_title FROM books WHERE price between 500 and 900 AND purchase_date < '21-JAN-2001' ORDER BY purchase_date;
B. SELECT book_title FROM books WHERE price IN (500,900) AND purchase_date < '21-JAN-2001' ORDER BY purchase date ASC;
C. SELECT book_title FROM books WHERE price < 500 or > 900 AND purchase_date < '21-JAN-2001' ORDER BY purchase date DESC;
D. SELECT book_title FROM books WHERE (price < 500 OR price > 900) AND purchase_date < '21-JAN-2001' ORDER BY purchase date DESC

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