For what value of aaa are the lines x+y=2x + y = 2x+y=2, x−y=0x - y = 0x−y=0, and ax+y=3ax + y = 3ax+y=3 concurrent?
a=1a = 1a=1
a=2a = 2a=2
a=3a = 3a=3
a=4a = 4a=4