4 ____ a certain doubt among the students as to the necessity of the work.A There has had B They had C There existed D It existed
39.When you read the book, you’d better made a mark ____ you have any questions.
___ she will join us in the game is not decided yet.
There are many sports lovers in his office.Some love climbing, ___ others enjoy fishing.
They can surely overcome those difficulties ___ they are closely united.
You’d better do ___ I told you.