it h - it i
- it happened shortly afterwards ...
- it has a rational, if not apparent explanation ...
- it has always been a problem that ...
- it has always been recognized that ...
- it has become a hindrance to changes ...
- it has become a source of error in research ...
- it has become fashionable to discuss ...
- it has been assumed that ...
- it has been found realistic to set ...
- it has been linked to ...
- it has been my intention to point out, through explanations and illustrations, that ...
- it has been popular to describe ...
- it has been the practice to use ...
- it has convinced me that this technique is the most effective for ...
- it has exactly the opposite meaning ...
- it has great possibilities ...
- it has limited most investigations of ...
- it has long been known that ...
- it has not proved possible, as yet, to obtain analytically the function ...
- it has quite a restricted application ...
