Jim has retired, but he still remember the happy time _______ with his students.
A. to spend B. spend C. spending D. spent
The little problems ______ we meet in our daily lives may be inspirations for great inventions.
A. that B. as C. where D. when
The national park has a large collection of wildlife, _________ from butterflies to elephants.
A. ranging B. range C. to range D. ranged
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
