______ awful day it was that day! We experienced _______ unusual weather in London.
A:What a; a
B:What an; an
C:What an; a
D:What an; /
小明为了寻找磁极间相互作用的规律,用条形磁铁和小磁针做实验,实验现象如图.据此得出磁极间相互作用的规律:同名磁极互相 ____,异名磁极互相 ____,此实验属于探索性的 ____实验.(填“定性”或“定量”)
一块黑板,长4米,宽1米.在它四周钉上木条边框,至少要用木条 ( )