Alice and Bob are travelling at two different constant velocities. In Alice's frame of reference, two explosions occur 1 second apart in time and 2 light seconds apart in space. If these two explosions occur time t apart and distance x apart in Bob's frame of reference, which statement is necessarily correct?
a) (ct)2>x2
b) (ct)2=x2
c) it is possible that t = 0
d) it is possible that x = 0
e) more than one of the options above is correct