The Two Stars near One Another Are Shown

Multiple Choice

The two stars near one another are shown. Positions of one member are shown relative to the other star at different times. From plots like this one, astronomers conclude that

A) the stars are in an elliptical orbit around one another.
B) the mass of the pair can be estimated.
C) one star is passing by the other never to return.
D) both the stars are in an elliptical orbit around one another.