Are the systems with transfer functions given below stable $($Does it become stable in any disturbance effect$)?$ Why? Find the $K_p,{}_p,$n and $$ values of these systems.

a$)\frac{-2\mathrm{.}5}{4s+1}$

b$)\frac{2}{2s^2-4s+1}$

c$)\frac{s+1}{5s^2+2s+1}$

d$)\frac{2s+3}{-4s^2+8s+1}$