the apple of sb.'s eye

1. 掌上明珠；珍愛物
   Her daughter is the apple of her eye.

   她女兒是她的掌上明珠。

apple of discord

1. 【書】爭端；禍根

• the apple of one's eye
  a person of whom one is extremely fond and proud. [orig. denoting the pupil of the eye, extended as a symbol of something cherished.]
• apples and pears
  Brit. rhyming slang stairs.
• a rotten (or bad) apple
  informal a corrupt person in a group, likely to have a detrimental influence on the others.
• upset the apple cart
  spoil a plan.