单项选择题

______,heat is produced.

A．Certain chemicals are mixed together
B．That certain 'chemicals are mixed together
C．Whenever certain chemicals are mixed together
D．The mixing together of certain chemicals

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热门试题

单项选择题

My pain ______ apparent the moment I walked into the room for the first man I met asked sympathetically: Are you feeling all right

A．must be
B．had
C．must have been
D．had to be

单项选择题

Being impatient is ______ with being a good teacher.

A．intrinsic
B．ingenious
C．incompatible
D．inherent