D
分析:根據(jù)3月份達(dá)到最高價(jià)9千元,7月份價(jià)格最低為5千元,得函數(shù)的振幅A=2且周期T=8.再根據(jù)函數(shù)的最大值為f(3)=9,算出φ=-

,從而得出函數(shù)表達(dá)式為f(x)=2sin(

x-

)+7,求出f(10)的近似值,即得國(guó)慶期間的價(jià)格.
解答:∵3月份達(dá)到最高價(jià)9千元,7月份價(jià)格最低為5千元,
∴2A=9-5=4,得A=2.函數(shù)的周期T=2(7-3)=8
因此,ω=

=

,得函數(shù)表達(dá)式為f(x)=2sin(

x+φ)+7
∵f(3)=2sin(

+φ)+7=9,函數(shù)最大值為9
∴

+φ=

+2kπ,得φ=-

+2kπ,(k∈Z)
∵|φ|<

,∴取k=0,得φ=-

,
由此可得函數(shù)表達(dá)式為f(x)=2sin(

x-

)+7
∴f(10)=2sin(

×10-

)+7=

+7≈8.4千元
即國(guó)慶期間的價(jià)格約為8.4千元
故選D
點(diǎn)評(píng):本題給出類似于三角函數(shù)的模型的實(shí)際應(yīng)用問(wèn)題,求一個(gè)近似值,著重考查了正弦函數(shù)的圖象與性質(zhì)的知識(shí),屬于基礎(chǔ)題.