Question 4If $a$ and $b$ are real numbers, which of the following expressions below must be non-negative?$a^2+b^2+a+b$$a^{2018}+b^{2017}$$a^4b^4+a^2b^2-1$$a^3b^3-2a^2b^2+ab$$a^2b^2+2ab+1$