Most birds find it safe to sleep in the trees, but ______ they have eggs or young chicks, they don’t use a nest.
_____ his knowledge of the mountainous country, John Smith was appointed as our guide.
Political parties often differ in their views on various _____ concerning their own countries.
Evidence obtained from observation and experiment is often used to _____ a scientific theory.
Jack is good, kind, hard-working and intelligent. _____, I can't speak too highly of him.
Because of the strong sun Mrs. William's new dining room curtains _____ from dark blue to gray within a year.