It is obvious ______ the local government can do to protect the environment for the next generations.
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
Many airlines now allow passengers to print their boarding passes online ______ their valuable time.
save
saving
to save
saved
Jane moved aimlessly down the tree-lined street, not knowing ______she was heading.
why
where
how
when
______ birds use their feathers for flight, some of their feathers are for other purposes.
Once
If
Although
Because