问题
单项选择题
已知某等差数列共有10项，其奇数项之和为15，偶数项之和为30，则其公差为（）。
A．5
B．4
C．3
D．2
答案
参考答案：C
解析：
a10-a9+a8-a7+a6-a5+a4-a3+a2-a1=5d-30-15
d=3，选C。
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已知某等差数列共有10项，其奇数项之和为15，偶数项之和为30，则其公差为（）。
A．5
B．4
C．3
D．2
参考答案：C
解析：
a10-a9+a8-a7+a6-a5+a4-a3+a2-a1=5d-30-15d=3，选C。
Language is colourful. There are many with heart. One of them is to “lose your heart” to someone. When that , you have fallen in love. if the person who “won your heart” does not love you, you are to have a “broken heart.” In your , you think that the person you loved is “hard-hearted,” and in fact, has a “heart of stone.” You may decide to “pour out your heart” to a friend. Telling someone about your personal can often make you feel better. If your friend does not to understand how painful your broken heart is, you may ask her to “have a heart.” You are asking your friend to show some sympathy (同情) for your . Your friend “has her heart in the right place” if she says she is sorry for you feel. If your friend says, “My heart bleeds for you”, she means the . She is a cold-hearted person who does not really your situation. When you are feeling , “your heart is in your mouth.” You might say, for example, that your heart was in your mouth when you asked a bank to lend you some money to a new house. If that bank says to you, do not “lose heart.” Be “strong-hearted.” Sit down with the banker and have a “heart to heart” talk. Be open and honest about your situation. The bank may have a “change of heart” and agree to lend you the money. Then you could worrying and “put your heart at rest.”
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