Every time _______ I come across difficulties, I will turn to my parents for help.

Many people like white as a color as it is a _____ of purity.

Teachers have to constantly update their knowledge in order to maintain their professional(专业的)_______.

We forgave his bad temper because we knew that his son's illness had put him under great _____.

It’s important for us to use a word or phrase according to the            in language studies.