His not coming our difficulties.
Just as the tree is the unit of a forest and the book the unit of a library, ______ the molecule is the unit of matter.
The door opened and in ________.
______ nobody was very enthusiastic about it, they decided to cancel the trip.
I think our boat can pass the treacherous water ______ cautiously handled.
The engineers are going on with their highway project, _____the expenses have risen.