The old man lives in that village house by himself, "by himself" probably means
A：alone
B：lonely
C：sadly
用反证法证明“在三角形中，至少有一个内角大于或等于60°”时，应先假设____．
阳春三月，油菜花开，眼下果实已成熟．由此推知，油菜属（ ）
