在于 zài yú to rest with; to lie in; to be due to (a certain attribute)(of a matter) to be determined by; to be up to (sb) Example sentences 关键在于你是否热爱你的工作？ guānjiàn zàiyú nǐ shìfǒu rè'ài nǐ de gōngzuò? The key is do you love what you do?