选出不符合本组类别的单词。
1._____________ shells, stamps, coins, since, dolls
2._____________ going, skating, dancing, roller blading, skiing
3._____________ marathon, contest, competition, computer, race
4._____________ ago, since, when, months, books
5._____________ beginner, lawyer, player, pro, champion
1.since 2.going 3.computer 4.books 5.pro