单项选择题
The basic causes are unknown, although certain conditions that may lead to cancer have been （）
A．identified B．guaranteed C．notified D．conveyed
单项选择题 All individuals are required to （）to the laws made by their governments.
单项选择题 They have always regarded a man of （）and fairness as a reliable friend.
单项选择题 Even when textbooks are （）through a school system, methods of teaching may vary greatly.
