The answer is:

b. It protects against four types of HPV.

The new HPV vaccine protects young women against four different types of HPV- 2 types that cause genital warts and 2 types that have been linked with cervical cancer. The vaccine works best in young girls who have not yet come in contact with these viruses. That's why the vaccine is recommended for all 11 and 12 year old girls as a routine vaccination and for all young women 13-26 years of age who have not yet had the vaccine. Girls and young women should receive the vaccine even if they have already had sex.