What is the biggest disadvantage of using the Internet for surveys?

Tea Party candidates running on the Republican ticket in 2010 demonstrated Duverger's Law:

that minor parties in a first-past-the-post system will usually converge with a major party. Indicate whether the statement is true or false

The best way to assure second-strike capabilities would be to keep all one's nuclear arms carefully hidden in the same place

Indicate whether this statement is true or false.