In the example sentence, I initially interpreted the sentence structure as 'We have seen that is about to rain.' However, the correct answer was 'seeing,' with the appropriate context being 'We see that it is about to rain.'
Alternatively, if the correct version is 'seeing,' the sentence could be 'We are seeing that it is about to rain.' Am I right? (I am aware that this is not feasible, but I theorized it.)
My question is; why was 'having seen' not the correct choice?
Seeing that it is about to rain, we had better leave now. (right answer)
Having seen that it is about to rain, we had better leave now. (my version)
(The question is also from a textbook named Building Skills for Proficiency, Cesur Öztürk, 57th Edition.)