suppose 在什么情況下要用虛擬語氣？如Nancy is supposed to (做完化學實驗)　at least two weeks ago.

你好！
supposing/suppose
作連詞，可以虛擬，可以不虛擬
suppose
that....后面不用虛擬的
supposing/suppose
something
should
go
wrong,what
would
you
do?
如有疑問，請追問。

Nancy
is
supposed
to
(做完化學實驗)　at
least
two
weeks
ago.
這句話不是用不用虛擬語氣，因為是不定時用現(xiàn)在時還是完成時的問題,單獨來看2種情況都可能成立，適用于不同語境下。
at
least
two
weeks
ago至少兩周以前，這句話有責備的含義，使用完成時表示她應該做什么（而沒做），2周前她就被告知做什么。Nancy
is
supposed
to
have
finished
the
chemistry
experiments
at
least
two
weeks
ago.
Nancy
is
supposed
to
finish
the
chemistry
experiments
at
least
two
weeks
ago.
責備的含義就弱了很多。差別在這里。
希望對你有所幫助。