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28. Don't leave Mary by_________. She is only one year old.

A. her         B. she       C. herself

27. Would you please pass me_________ sugar on the table?

A. a        B. the        C. /

26. I'm afraid there_________much time left. Let's hurry.

A. isn't        B. aren't        C. is

(1)如果折痕FG分別與AD、AB交與點F、G(如圖1)，，求DE的長；

 (2)如果折痕FG分別與CD、AB交與點F、G(如圖2)，△AED的外接圓與直線BC相切，

  求折痕FG的長．