Mystery Trivia Tuesday: Sherlock Holmes on Crime

Can you name the Sherlock Holmes stories in which the following quotes on crime were written?

1.  "As you are aware, Watson, there is no one who knows the highest criminal world of London so well as I do."
2.  "I choose to be only associated with those crimes which present some difficulty in their solution."
3.  "The larger crimes are apt to be the simpler, the bigger crime, the more obvious, as a rule, is the motive."
4. "I read nothing except the criminal news and the agony column. The latter is always instructive."