When _____ why he walked in _____ permission, he just _____ at us and said nothing. 

Birds singing is sometimes a warning to other birds        away.

In Europe unemployment hit a new record with young people __________ it harder to get jobs．

Dr Yuan makes______ possible______ one-third more of the crop in the same fields.

 ______ as the “First Lady of Speech”, Dr Lillian Glass is recognized as one of the world’s leading experts on communication skills.