A:①②
B:①④
C:②③
D:②④
读一读,选出不同类的单词。
____A. sheep B. ship C. train D. car
____A. bike B. bed C. bus D. plane
____A. listen B. hear C. see D. monster
____A. big B. mouth C. small D. long
____A. green B. white C. red D. rabbit
已知a→与b→为两个不共线的单位向量,若向量a→+b→与向量ka→﹣b→垂直,则实数k=____