But the first stage is to acquire a suitable image from the middle frame of each pallet car. In the next section, .....
Which is better for the blank
- we propose a method for this purpose.
- we propose a method to do this.
- we propose a method for this.
- we propose a method for it.
Sometimes I don't know which noun is suitable to refer to an already mentioned thing. then I may just use "this". Is it common in writing in English? or is it better to always find a suitable noun after "this", like this purpose, this task, this job. what are common words for these occasions?