It never occurred to humans until the mid-1990s ______ some animals can be cloned.
In my opinion, what he told us just now about the affair simply doesn’t make any________.
He ____the job well, but he_______so careless.
---You should have thanked her before you left. ---I meant _______. But when I was leaving I couldn’t find her anywhere.
It is thought that one billion people I the world, ________is half the word’s workers, earn their living by farming.
Our teacher is always busy preparing lessons until 11 o’clock at night, _______we students have gone to sleep.