Which lens would you use

You have one of each of the following lenses, all large diameter: f= 50mm, f= 100mm, f= 200mm, f= 25mm, f= -50mm. Which of them would you use, and why (ignoring aberrations) if you were making:

a. a magnifying glass?
b. a compound microscope?
c. an astronomical telescope?
d. a Galilean telescope?

a. 50mm
b. 25mm
c. 200mm
d. 100mm

Essentially, if the distance is longer, it is suggested to use a longer focal length since this will define how close you can get to an object, magnification wise and focus wise.

Hope I helped.