A car engine cannot run smoothly without motor oil.____ our body cannot function efficiently without vitamins.

-- You seem to be burning yourself out with so much work!-- ______. I'm dying for a thorough rest and a good workout.

It’s always difficult to live in a foreign country, ______ when you don’t speak the language. 

What he did ______ what he said moved us. 

I think the answer is right but I’m not ____ sure about it.