He doesn't __________ to have many friends.
A:look
B:sound
C:seem
D:smell
光从空气垂直射入水中,折射光线与反射光线的夹角为( )
①鉴别一株小麦是否为纯合子
②鉴别一只白兔是否为纯合子
③鉴别一对相对性状的显隐性关系
④不断提高水稻品种的纯合度