Here's the solution to the exercise:
1) You've been very **silent** today. What's the matter?
*Explanation*: 'Silent' fits best as an adjective describing someone's unusual behavior.
2) Killing a person is a terrible **crime**.
*Explanation*: 'Crime' is the most suitable noun to describe the act of killing someone.
3) Nowadays people prefer big-**screen** televisions.
*Explanation*: 'Screen' makes the most sense when talking about television preferences.
4) The car disappeared **within** behind the houses.
*Explanation*: The best word here is "within" to describe the car disappearing from sight.
5) The new test showed much better **achievements** of the students.
*Explanation*: 'Achievements' aligns with the idea of improved test results.
6) There are some very talented young film **directors** working in the country.
*Explanation*: 'Directors' fits the context of the film industry.
7) I think I'll be able to complete the work **within** two or three days.
*Explanation*: 'Within' implies a time frame.
8) I can go **anywhere** with you if you just ask me.
*Explanation*: 'Anywhere' suggests a place that the speaker is willing to go.