题干
Mr Jackson hasn't decided this weekend.
A：where he will have a picnic
B：where will he have a picnic
C：where he had a picnic
D：where did he have a picnic
答案(点此获取答案解析）
A
，则△ABC必是等腰三角形；
，则△ABC必是直角三角形；
，则△ABC必是钝角三角形；
，则△ABC必是等边三角形。