What is an example of f(-x)=f(x) for all real numbers x?

Which of the following are independent events? a) knowing that it is going to rain tomorrow, and bringing an umbrella to schoolb) knowing that you have to get up early tomorrow, and going to bed before 9 p. mc) knowing that it is going to rain tomorrow, and going to bed before 9 p. md) knowing that you have a test in school tomorrow, and studying thw night before