(Avatar changed just for Santa's birthday) 
As for #3, these exercises are rarely intended for serious topics, but the answer might include hunger, poverty, etc., if it asked something like "¿qué te llama la atención de la vida?"/"¿qué te extraña/asombra/intriga de la vida?".
By the way, if you said "los adolescentes son
lo curioso de la vida", you would be saying that you'd find it funny that they exist.