It is difficult for us to imagine_____ life was like for slaves in the ancient world.
Jim has retired, but he still remember the happy time _______ with his students.
to spend
spend
spending
spent
The little problems ______ we meet in our daily lives may be inspirations for great inventions.
that
as
where
when
The national park has a large collection of wildlife, _________ from butterflies to elephants.
ranging
range
to range
ranged
In the 1950s in the USA, most families had just one phone at home, and wireless phones _______ yet.
haven't invented
haven't been invented
hadn't invented
hadn't been invented
If you don't understand something, you may research, study, and talk to other people _______ you figure it out.
because
though
until
since