1to rest with; to lie in; to be due to (a certain attribute)
2(of a matter) to be determined by; to be up to (sb)
Examples
xué学zhōng wén中文zuì最kùn nan困难de的bù fen部分zài yú在于hàn zì汉字。
学中文最困难的部分在于汉字。
The hardest part of learning Chinese is the Chinese characters.
演出的成功，在于大家的团结努力。
Everybody's hard work contributed to the show's success.
电视的优点在于它给体育爱好者提供了更大的方便。
Television has the advantage of providing sports fans with greater convenience.