已知y=lncosxy = \ln\cos xy=lncosx,则d2ydx2=\dfrac{d^2y}{dx^2} =dx2d2y=( ).
(A)tanxsecx\tan x \sec xtanxsecx
(B)−tanxsecx - \tan x \sec x−tanxsecx
(C)−sec2x - \sec^2 x−sec2x
(D)sec2x\sec^2 xsec2x
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