Scientists have created GM tomatoes which ______ fresh for 45 days, three times as long as normal tomatoes.
The moment she heard of the news that her son was involved in the crime, she ______ pale.
I didn't see you at the meeting. If you ______ , you would have met my brother.
Don't use words and expressions or phrases ______ only to people with specific knowledge.
Emergency line operators must always ______ calm.
After 15 years in the USA, he has finally decided to American ______ citizenship.