_____ his knowledge of the mountainous country, John Smith was appointed as our guide.
The driver who died in the accident could have ________, but he was sent to hospital too late.
The patient’s progress was very encouraging as he could ________ get out of bed without help.
In my opinion, your composition is not as interesting as his but yours is ________ in writing.
---We all had a lot of fun at the barbecue yesterday. Pity you weren’t there. ---I really should have gone with you, but I ________ on some remaining problems.
If you want to study the nature of the universe, first of all, you must be clear about its ________.