21.Among the trees left over after the planting is done
there must be
（A）at least one maple
（B）at least one red oak
（C）at least one sycamore
（D）at most one maple
（E）at most one red oak
22.If maples are planted， the side of the street that has
four trees must have
（A）red oaks in positions 1 and 7
（B）red oaks in positions 3 and 5
（C）sycamores in positions 1 and 3
（D）sycamores in positions 1 and 7
（E）sycamores in positions 3 and 5
23.A list of the fifteen operas most frequently performed
in recent times includes no works by the nineteenth-
century German composer Richard Wagner. Although
music producers tend to produce what audiences want，
relative infrequency of performance probably does
not indicate lack of popularity in Wagner's case， since
Wagner's operas are notoriously expensive to perform
Which of the following， if true， most strongly
supports the conclusion of the argument above？
（A）The list of most frequently performed operas
does not include operas produced by small
（B）Some opera companies are backed by patrons
who are willing to commit large sums of
money in order to enjoy lavish productions.
（C）All of the fifteen most frequently performed
operas of recent times are works that have
been popular for at least 75 years.
（D）More recordings have been produced recently of
the works of Wagner than of the works of any
other composer of opera.
（E）Operatic works of all kinds have been increasing
in popularity in recent years.
24.The bodies of dwarf individuals of mammalian
species are generally smaller in relation to those of
nondwarf individuals than are the teeth of the dwarf
individuals in relation to those of the nondwarf indi-
viduals. Fragmentary skeletal remains of an adult
dwarf woolly mammoth were recently found. The teeth
are three-fourths the size of the teeth of an average
adult nondwarf woolly mammoth.
The statements above， if true， most strongly support
which of the following？
（A）The body of the dwarf woolly mammoth was
less than three-fourths the size of the body of
an average adult nondwarf woolly mammoth.
（B）None of the teeth of the dwarf woolly mammoth
that were recently discovered was as large as
any of the teeth of nondwarf woolly mammoths
that have been discovered.
（C）The teeth of most adult dwarf individuals of
mammalian species are three- fourths the size of
the teeth of the adult nondwarf individuals of
the same species.
（D）Dwarf woolly mammoths had the same number
of teeth as did nondwarf woolly mammoths.
（E）Dwarf individuals of most mammalian species
are generally no more than three-fourths the
size of the adult nondwarf individuals of those