Constant Function

Q. Which of the following graphs represent a constant function?

1. Only $\left(1\right)$ and $\left(4\right)$
2. Only $\left(1\right),\left(2\right)$ and $\left(4\right)$
3. Only $\left(1\right)$ and $\left(2\right)$
4. Only $\left(1\right)$

Q. Which of the following statements is (are) CORRECT for a constant function?

1. It is a function whose range consists of only one element
2. It is a type of polynomial function having degree $0$
3. Its graph is a line which is always parallel to $x-$axis.
4. Domain of constant function is $R$

Q. If f(x) be a continuous function (a function whose graph has no breaks) defined for $1\le x\le 3.f\left(x\right)ϵQ\forall xϵ[1,3]andf\left(2\right)=10$ (Where Q is a set of all rational numbers). Then, f(1.8) is

1. 1
2. 5
3. 10
4. 20