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

整个排序过程都在内存中进行的排序，称为______。