问题
[$\textcolor{Orange}{\int \frac{1}{\cos ^{2} x} \mathrm{d} x}$] 的积分该怎么计算？选项
[A]. $\int$ $\frac{1}{\cos ^{2} x}$ $\mathrm{d} x$ $=$ $\tan x$[B]. $\int$ $\frac{1}{\cos ^{2} x}$ $\mathrm{d} x$ $=$ $\tan x$ $+$ $C$
[C]. $\int$ $\frac{1}{\cos ^{2} x}$ $\mathrm{d} x$ $=$ $\cot x$ $+$ $C$
[D]. $\int$ $\frac{1}{\cos ^{2} x}$ $\mathrm{d} x$ $=$ $- \tan x$ $+$ $C$
$$\int \textcolor{Red}{\frac{1}{\cos ^{2} x}} \mathrm{d} x =$$ $$\textcolor{Red}{\tan x} + \textcolor{Yellow}{C}.$$