Show me the steps to solve

For each system below: Is it causal? Memoryless?

a$.y(t)=u(t-1)$

b$.y(t)=a_{0}u(t)+a_{1}u(t+1)$

c$.y(t)={\displaystyle \underset{l-1}{\overset{t+1}{}}}u()d$

d$.y(t)={\displaystyle \underset{}{\overset{l}{}}}u({)}^{2}d$