please help me to solve this question

For which values of ( a ) will the system of equations

x+y=0

x+2y+(a+3)z=0

x+y+(a+1)z=a^2 - 1 ( a square minus 1 )

has :

1 - A unique non-zero solution

2- No Solution

3- A trivial solution

4- infinitely many solutions

please i need a little bit of explanation on that