VCB nào sau đây là bậc 1?

\[{\alpha _1}\left( x \right) = \sin 2x - 2\sin x\]

\[{\alpha _3}\left( x \right) = {e^{\sin x}} - \cos x\]

\[{\alpha _4}\left( x \right) = \sqrt {1 + 2x} - 1 - \sqrt x \]

\[{\alpha _2}\left( x \right) = \arcsin \left( {\sqrt {4 + {x^2}} - 2} \right)\]