Air, carbon dioxide, and other gases are examples of which of the following types of contrast media that will appear dark on an X-ray?

An economic system where all or most businesses are owned by government

Name three things the framers of the constitution did to keep the federal government or any part of it from becoming too powerful.

In the years after world war ii, which of the following caused many people from asian and african countries to migrate to europe? a. the end of the soviet union b. new economic opportunities after colonialism ended c. the religious freedom found in europe d. new laws allowing greater numbers of immigrants into european countries