At times the balance in nature is ______ , resulting in a number of possibly unforeseen effects.
I couldn't __________. The line was busy.
They are building the dam in __________ with another firm.
(2012·上海) The club, __________ 25 years ago, is holding a party for past and present members.
(2012·山东) After completing and signing it, please return the form to us in the envelope __________.
"It’s sucha nice place," Mother said as she sat at the table __________ for customs.