The scientists were trying to look for all possible _______ as to where this species came from.

Mr Black, who is a ______, is in love with Miss Smith, who is a ______.

I bought a dress for you only 10 dollars in a sale; it was a real _____.

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

Due to the widespread________ of this medical technology, more diseases can be discovered and treated at an early stage.