TASK 1.
We imagine we need to move the rocks, in a virtual dimension. For this, we match four pieces of talk with four short words. Only then, the rocks will give way.

We can call the short words prepositions, in schoolspeak. Prepositions may tell where something is. Use your language intuition.

The four pieces of talk:
I think.
I am thinking.
I have thought.
I have been thinking.

The four short words:
TO    ON    AT    IN

I have done one for you:
TO    I have thought.

Think, if the short words would match different, if we said,

I thought.   /   I will think.
I was thinking.   /   I will be thinking.
I had thought.   /   I will have thought.
I had been thinking.   /   I will have been thinking.


I don't know about you, but we're lively kids. We swim, hike in mountains, and Bob even wants to go to the Himalaya, so he does not believe in the Unreal Past anymore, he says, because he does not care to have any Unreal Future.

We have thought up a River of Time. It is impossible to get over without the Stones of Time. We have patterns that emerge with those. Try to match the short words, TO, ON, AT, and IN, and the patterns.

We can see the answers with the generative grammar here.