Pg 521 (453) - Q21
You can immediately rule out E because the two circles overlap, so
S has points in common with T and violates rule 1. Rule 2 requires
that any line segment drawn with endpoints in S cannot intersect with any
line segment that can be drawn with endpoints
in T; if you think about this, this means that any segment drawn
with endpoints in S cannot touch T. In B, if you drawn a segment
from one tip of moon-shaped S to the other tip, you will cross over T.
In C, if you drawn a segment through the top part of S,
you will go over T. Similarly, in D, if you draw a segment
along the diameter of the outer circle of S, you will cross T. The
only figure that meets the requirements of being “unlinked” is A, for which
S and T do not share any points, and you cannot drawn
a segment in either that would touch the other. The answer
is A.