Lee contributed fifty dollars, but he wishes he could contribute ________.

It is gravity ________ objects toward the earth.

Using a globe can be ________ it is educa-tional.

"Forty-niners" ________ to California for gold in 1848.

________ many of the designs for the new capital were considered lost forever, Benjamin Banneker helped reproduce the original plans.

The wheel, ________ has remained important for 4,000 years, is one of mankind's first inventions.

________ has improved a lot since she started her new job.

I know ________ a different way to get there but I like this one.

Physical fitness exercises can cause injuries ________ the participants are not careful.

Although solar energy is cheaper than oil, ________ have advantages as well as disadvantages.