of p - one
- of prime interest in ... is ...
- of rare occurence ...
- of special interest are the reasons for the development of ...
- of the whole (book, article) ...
- often, ...
- on (upon) condition that ...
- on rare occasions ...
- on sevaral occasions ...
- on the (или an) average ...
- on the contrary ...
- on the eve of ...
- on the other hand, ...
- on the principle that ...
- on the whole, ...
- on the whole, it is not yet clear ...
- on this evidence, ...
- on thе/ an average ...
- once and for all ...
- once the limit is established, it remains to compute ...
- once the results are studied scientists will have a complete body of knowledge about ...
