In the figure above, comparing the two competing hypotheses for the evolutionary relationships among ...

In the figure above, comparing the two competing hypotheses for the evolutionary relationships among mammalian groups:
 
  a. the placentals and marsupials are sister groups under the Theria hypothesis, and the monotremes and marsupials are sister groups under the Marsupionta hypothesis.
  b. the monotremes and marsupials are sister groups under the Theria hypothesis, and the placentals and marsupials are sister groups under the Marsupionta hypothesis.
  c. the monotremes and marsupials do not form sister groups under either the Theria hypothesis or the Marsupionta hypothesis.
  d. the monotremes and marsupials form sister groups under both the Theria hypothesis and the Marsupionta hypothesis.