如图所示，电源电动势为ε，电源内阻为r，当电键K闭合时，正确的判断是（   ）

如图，在△ABC中，∠BAC=90°，AD是中线，E是AD的中点，过点A作AF∥BC交BE的延长线于F，连接CF．

（1）求证：AD=AF；

（2）如果AB=AC，试判断四边形ADCF的形状，并证明你的结论．

Dunnottar Castle (城堡)

    Castle open times:

    Summer season: (April 1^st - September 30^th ) 9:00-5:30 every day.

    Winter season: (October 1^st -March 31^st )

    Oct 1^st - Oct 28^th 10:00-4:30

    Oct 29^th -Nov 11^th 10:00-3:30

    Nov 12^th -Nov 25^th 10:00-3:00

    Nov 26^th- Jan 20^th 10:00-2:30

    Jan 21th-Feb 3^rd 10:00-3:00

    Feb 4^th- Feb 17^th 10:00-3:30

    Feb 18^th- Feb 24^th 10:00-4:00

    Feb 25^th- Mar 31^st 10:00-4:30

    Bad Weather Conditions:

    Before going to the Castle, we advise you to visit our website(www. dunnottar.com)to make sure that the Castle is open. On the days of bad weather, the castle may be closed for safety reasons.

    Prices:

    Adult ticket:

    Children ticket:

    Guide Book:

    Buy tickets at the door.

    We do not offer pre-booking(预定)for tickets.

    Castle Closure Dates:

    The Castle will be closed on the following dates-25th of December and the 1^st 2^nd of January.

    Post code: AB39 2TL

    Dogs: Dogs are welcome at the Castle as long as they are kept on a leash(皮带) at all times.