It is the prevention of disease______its successful treatment that has led to the rapid increase of the world’s population.
We stood_______ to the strange-looking animal so that we could watch it_______.
_______in the wall behind the kitchen, the door was hard to find.
The old professor gave a long _______ lecture, and made us so _______ that we all felt sleepy.
Climbing onto the top of the mountain,_______.
The flowers_______ sweet in the botanic garden attract the visitors to the beauty of nature.