The last digit of $5^n$ is . . . . . . ,where $n \in N$.

Which of the following is not a polynomial in variable $x$?

For two consecutive positive integers $a$ and $b$,what is the value of $\text{HCF}(a, b) \times \text{LCM}(a, b)$?

The number $3 \times 15 \times 11 + 11$ is a . . . . . . number.

The product of any four consecutive positive integers is always divisible by . . . . . . .

Check whether $4^n$ can end with the digit $0$ for any positive integer $n$.