Exercise 2 solution

(a) Closed rings rising from 300 to 330 towards the middle: a summit (a hill
    top), with the top a little above 330 m.

(b) V shapes with the points aiming uphill (towards 120) and a stream along
    the middle: a valley. The stream confirms it, because water runs along
    the lowest ground.

(c) V shapes with the points aiming downhill (towards 100) and no stream: a
    ridge, or a spur if it is a small tongue coming off a bigger hill.

(d) Two sets of higher rings with a gap at 350 m between them: a saddle
    (col). It is the lowest point on the ridge joining the two tops, and
    often the easiest place to cross.

Check for valley or ridge: look at which side the higher numbers lie and
whether a stream is present.