单项选择题

Which of the following is TRUE

A．The various petroleum products are produced by filtration.
B．Heating and condensation produce the various products.
C．Chemical separation is used to produce the various products.
D．Mechanical means such as the centrifuge are used to produce the various products.

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单项选择题

Many thousands of hydrocarbon compounds are possible because______.

A．the petroleum products vary greatly in physical appearance
B．complicated refining processes rearrange the chemical structure
C．the two atoms in the molecule assume many positions
D．the pressure needed to force it to the surface causes molecular transformation

单项选择题

What is implied by the author

A．Shiftwork had a direct effect on the attitudes and behavior of family members.
B．Shiftworkers could live a normal life.
C．Shiftwork couples had unconventional ideas about marriage.
D．Female shiftworkers were satisfied with the time spent together with their families.