Which of these natural processes can we actually see taking place?

the development of a valley

tectonic action between two plates

the development of a mountain

the growth of a forest

the growth of a glacier

all of the above

none of the above

The correct answer is - all of the above.

The development of a valley can easily be witnessed at certain places on the planet, even though there will be minor changes in a lifetime of a human, still if observed carefully, slight changes can be seen.

The tectonic action between the plates is seen and experienced every day in multiple parts of the world, and the reason for that is the volcanic activity and the earthquakes.

The mountains grow pretty slowly, from 1 mm up to several cm in a year. So if take an average lifespan of a human, slight changes can be seen in the landscape. If its 1 mm growth it can be 8 cm change in a an average lifespan, or if its 5 cm annually, it can be a change of 4 meters.

The growth of a forest is the easiest to see, because the trees grow quickly, and only few years a barren land can be totally turned into a forest.

With slight drop of temperatures on certain places, the water will start to freeze, and the formation of glacier can take only few years, so objectively it is something that can be seen.