Но он не мог долго думать об этом,

Но он не мог долго думать об этом, таk как был очень занят:

Results (English) 1:

But he could not think of this for a long time, tak as was very busy:

Results (English) 2:

But he could not think long about it, as tak was very busy:

Results (English) 3:

But he could not for a long time to think about this, таk as had been very busy.