_____ medicine works in a human body is a question ____ not everyone can understand fully.
My friend David was not used _______ by air, so he felt unwell(不舒服).
We stopped on our way to London for _____.
____ that caused him to serve dinner an hour later than usual.
China ________ a sharp increase in the number of aged people over the past decade.
Today, we’ve discussed a number of large summer gatherings for feasts and celebrations _____the Inuit usually swap stories.