In each question below, a sentence is given with a part of it printed in bold type. That part may contain a grammatical error. Each sentence is followed by phrases 1), 2), 3) and 4). Find out which phrase should replace the phrase given in bold to correct the error, if there is any, and to make the sentence grammatically meaningful and correct.  The hills are also a crucial linking in the eras that Buddhism flourished in this part of the country.