《孟子》云：“不违农时，谷不可胜食也”；“斧斤以时入山林，材木不可胜用也”。这表明[ ]

A．自然界的变化是有规律的

B．客观规律是可以被认识和改造的

C．自然界的发展规律是客观的

D．改造世界必须遵循客观规律

The principal advantage of NAVTEX radio warnings is that（）.

A.they can be used by mariners who do not know Morse code

B.only an ordinary FM radio is necessary to receive these warnings

C.information on a given topic is only broadcast at specified times

D.they cover a broad spectrum of the radio band allowing reception on almost any type of receiver