单项选择题

The machine ______, the next step was how to operate it.

A．having been installed
B．had been installed
C．having being installed
D．has been installed
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Outline:1自然灾害频繁发生，给人类带来了巨大的损失。2在自然灾害面前，我们该怎么做Words for reference:development, harm, blind, earthquake, drought, harmoniousNatural Disasters
单项选择题
Those who want to get the information about flight schedule should ______ at the booking office.
A．acquire
B．request
C．inquire
D．require
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