Classify the following polynomial as linear, quadratic, cubic and biquadratic polynomial.

$2+3x$

Classify the following polynomial as linear, quadratic, cubic and biquadratic polynomial.

$y^4$

Classify the following polynomial as linear, quadratic, cubic and biquadratic polynomial.

$3z$

Classify the following polynomial as linear, quadratic, cubic and biquadratic polynomial.

$x-x^3$

Classify the following polynomial as linear, quadratic, cubic and biquadratic polynomial.

$x+x^2-x^4+3x^3-2$