设f（x），g（x）在[a，b]上连续，且满足∫axf（t）dt≥∫axg（t）dt，x∈[a，b），f（t）dt=∫abg（t）dt。证明∫abxf（x）dx≤∫axxg（x）dx。
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Now listen to the following recording and answer questions 16 to 19.
A. Quiet and confident.
Bold and loud.
C. Shy and energetic.
D. Tricky and timid.
微分方程y"+y=e—xcosx满足条件y（0）=0的特解为________。
已知某土饱和密度为2.38g/cm3，水密度为1g/cm3，则该土浮密度为______。
A. 2.38g/cm3
B. 3.38g/cm3
C. 1.38g/cm3
D. 2.06g/cm3
Now listen to the following recording and answer questions 20 to 22.
Alcohol use will cause diseases.
B. Women chink more than men.
C. Europe has the highest alcohol use.
D. Alcohol is addictive to everyone.
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