—That's a nice mobile phone.
—It is. My aunt __________ it for my last birthday.
A:buy
B:will buy
C:have bought
D:bought
如图,在Rt△ABC中,∠A=90°,BD平分∠ABC,交AC于点D,若AB=4,且点D到BC的距离为3,则BD=____.
冬天坐在火炉旁取暖,主要利用的是( )