下列动物中属于哺乳动物，但却不是胎生的是    (    )

A．东北虎

B．鸦嘴兽

C．海豚

D．蝙蝠

Which of the following is true, according to the passage

A．Email shows more authority than other products of digital technology.

B．Email is as fragile a thing as it is convenient to its users.

C．Email can keep as many as 1,500 saved messages.

D．Email may help strengthen your own memory.