I have experienced quite a number of cases ______ Ireally wanted to help but could not find anything to _______.

Mr.Black is an experienced engineer，and he will be employed to __________ us in improving our equipment.[ ]

er Li Keqiang delivered a speech at the conference, _________ university graduates to start their own business.

It’s raining heavily, isn’t it?–Yes, ______ yesterday.

It’s a hard ______ to do so much_____ every day.