Answer: B. tu
Explanation: You use Vous when talking in a formal way, or when talking to multiple people, You use Je when talking about yourself, and you use Tu when talking informally or to a friend. The words tu and vous both mean you. In English, the word you can be used to address any person or number of people, whatever the age, social status etc of that person. In French, which word for you is used depends on the person being addressed (spoken/written to).
A common misconception is that "tu is used for talking to children and vous for talking to adults" or "tu is for friends and vous is for strangers". If this was the whole truth, life would be nice and simple and we could all go away and have a cup of tea rather than reading web pages about when to use tu and when to use vous (and I wouldn't have to write one...). As we'll see below, the reality is a bit more complex. For example, there are situations where two adults meeting for the first time will automatically use tu, and cases where an adult will address a child as vous.