16.If Jones is to sing immediately before Harris sings，
which of the following must be assigned to time
17.If McIntyre is to sing immediately before Strapp
sings， Trevino could be assigned to which of the
following time slots？
18.If McIntyre is assigned to time slot 4， which of the
following must be true？
（A）Harris is assigned to a lower-numbered time slot
（B）Jones is assigned to a lower-numbered time slot
（C）Nelson is assigned to a lower-numbered time
slot than McIntyre.
（D）Strapp is assigned to a lower-numbered time slot
（E）Trevino is assigned to a lower-numbered time
slot than Jones.
Along a street that is currently without trees， seven trees are to be planted in the pattern
1 3 5 7
2 4 6
Where each number designates the position of a tree. No
more than two kinds of trees can be planted. If maples
are used， no maple can be planted adjacent to or immedi-
ately diagonally opposite another maple. Two trees are
adjacent to each other if the numbers of their positions
differ by two， and immediately diagonally opposite if
their numbers differ by one. The following trees， of three
kinds， are available for planting：
Three red oaks
19.Which of the following can be the trees planted along
the side of the street that has four trees， in order of
their positions beginning with position 1？
（A）Maple， sycamore， maple， sycamore
（B）Maple， sycamore， red oak， maple
（C）Red oak， maple， maple， red oak
（D）Sycamore， sycamore， maple， maple
（E）Sycamore， sycamore， red oak， red oak
20.If red oaks are used， then which of the following
must be true？
（A）The other trees used are all maples.
（B）The other trees used are all sycamores.
（C）The red oaks are in positions 1， 2， and 3.
（D）The red oaks are in positions 3， 4， and 5.
（E）The red oaks are in positions 4， 5， and 6.