Question 9
For Numbers 7-10:
A number of species faced extinction during the Mesozoic era. Species R, S, T, U, V, W, and X were species that all became extinct during this era, and scientists have determined that their extinctions occurred based on the following constraints:
W became extinct before X. U became extinct after T.
S became extinct before T. X became extinct before U. V became extinct after U.
S became extinct before W.
R became extinct before S.
Which is the smallest number of species that could have gone extinct before T?
A number of species faced extinction during the Mesozoic era. Species R, S, T, U, V, W, and X were species that all became extinct during this era, and scientists have determined that their extinctions occurred based on the following constraints:
W became extinct before X. U became extinct after T.
S became extinct before T. X became extinct before U. V became extinct after U.
S became extinct before W.
R became extinct before S.
Which is the smallest number of species that could have gone extinct before T?