People often have this belief _______ development is bad for the environment, but this does not have to be true.
| A．whether | B．what |
| C．that | D．how |
In the 1950s in the USA, most families had just one phone at home, and wireless phones _______ yet.
| A． |
haven't invented |
B． |
haven't been invented |
| C． |
hadn't invented |
D． |
hadn't been invented |
If you don't understand something, you may research, study, and talk to other people _______ you figure it out.
| A． |
because |
B． |
though |
C． |
until |
D． |
since |
Many airlines now allow passengers to print their boarding passes online ______ their valuable time.
| A． |
save |
B． |
saving |
| C． |
to save |
D． |
saved |
Jane moved aimlessly down the tree-lined street, not knowing ______she was heading.
| A． |
why |
B． |
where |
C． |
how |
D． |
when |
______ birds use their feathers for flight, some of their feathers are for other purposes.
| A． |
Once |
B． |
If |
C． |
Although |
D． |
Because |