There was a time when a C meant average. The average GPA at four-year colleges and universities has risen from 2.52 in the 1950s to 3.11 in 2006. And according to Stuart Rojstaczer, a former Duke University professor and founder of GradeInflation.com, GPAs only keep rising. At some colleges, Rojstaczer says, over 50% of the grades given are A's.
Trench warfare was caused by an advance in defensive weaponry. The machine gun was too heavy to be used as a mobile weapon, and therefore was placed into a fixed position. Barbed and concertina wire was also heavily used.
Trenches are geological features formed by convergent boundaries. When two tectonic plates converge, the heavier plate is forced downward, creating a subduction zone. This process results in the formation of a trench. The Marianas Trench is an example of a trench formed by the convergence of two oceanic plates.