Answer:
The correct option is D.
Step-by-step explanation:
If function f(x) is called an even function if f(-x)=f(x).
The first function is

Put x=-x,
![[\because \sin(-x)=-\sin x]](https://tex.z-dn.net/?f=%5B%5Cbecause%20%5Csin%28-x%29%3D-%5Csin%20x%5D)
So, this function is not an even function.
The second function is

Put x=-x,

So, this function is not an even function.
The third function is

Put x=-x,

So, this function is not an even function.
The fourth function is

Put x=-x,
![[\because \cos(-x)=\cos x]](https://tex.z-dn.net/?f=%5B%5Cbecause%20%5Ccos%28-x%29%3D%5Ccos%20x%5D)
So, this function is an even function.
Hence the correct option is D.