Sperm penetration tests check to see whether a man's sperm can move through cervical mucus and the fallopian tubes to join with (fertilize) an egg. This test is usually done when a couple is having trouble becoming pregnant (infertility). There are different sperm penetration tests.
The idea that a boundary is shifting can be applied to different areas. A shifting frontier of science would be referring to the fact that science is always changing and growing, and always with new areas. In wartime, a shifting frontier would be an international border which is constantly being renegotiated.
Second Grade, Westward Expansion 2005 Colorado Unit Writing Project 3 C. Key Vocabulary 1. Westward Expansion occurred around 1780-1890 when pioneers moved west over the Great Plains and Rocky Mountains toward the Pacific Ocean. 2. Pioneers were settlers who were among the first to move to the American Frontier. 3.