Which of the following is the most accurate statement about the relationship between gene duplication and mobile genetic elements?

A) The most common way that genes are duplicated is by the activity of mobile genetic elements.
B) A duplicated gene is an example of one kind of mobile genetic element.
C) Mobile genetic elements can cause gene duplication, but most gene duplication events are caused by other mechanisms.
D) Gene duplication is one kind of genomic defense against the spread of mobile genetic elements.