There's the next sentence:
"I saw Mr Brown ..... the building at two o'clock."
leave / to leave / having left
Which option would be the most appropriate to put in and why ? I really want to put in "was leaving", but there's no such option.
"to leave" - certainly no, there's no necessity in infinitive there.
"having left" - something strange, I don't know what is it.
- 'leave' - may be 'saw' already indicates Past tense and we don't need to do that again. but why is there no ['s] ending for (he\she\it) ? is it acceptable to use bare infinitive with he\she\it without gerund or any modal verb.