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分别与AD、AB交与点F、G(如图1)，，求DE的长；

 (2)如果折痕FG分别与CD、AB交与点F、G(如图2)，△AED的外接圆与直线BC相切，

  求折痕FG的长．