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
—______ that company to see how they think of our product yesterday?
—Yes. They are happy with it.
A. Did you call B. Have you called
C. Will you call D. Were you calling
