7.
如图,CD为△ABC的中线,且CD⊥AC,O为BC边上一点,以O为圆心,0C为长半径作⊙O,若⊙O与AB恰好相切于点D,则tanB=( )
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| A. | $\frac{1}{3}$ | B. | $\frac{\sqrt{2}}{4}$ | C. | $\frac{3}{8}$ | D. | $\frac{1}{2}$ |