- halen = to fetch, to go for
- krijgen = to recieve, to get
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Just learning myself, but will try an explanation. Krijkt means for something to come into your possession, like you might get a cookie.
Haalt means to fetch, to call for, to pick up... The thing you are getting is not something you will possess. In this case you summons the Dr but you won't possess him or her.
Why is it not correct to say"The boy collects a doctor quickly?'' Also why is bellen not used?