客运专线双块式混凝土轨枕，混凝土胶凝材料用量应不超过（）kg/m3。

A、500；

B、490；

C、480。

MIDI enables people to use (11) computers and electronic musical instruments. There are actually three components to MIDI, the communications" (12) .", the Hardware Interface and a distribution (13) called "Standard MIDI Files". In the context of the WWW, the most interesting component is the (14) Format. In principle, MIDI files contain sequences of MIDI Protocol messages. However, when MIDI Protocol (15) are stored in MIDI files, the events are also time-stamped for playback in the proper sequence. Music delivered by MIDI files is the most common use of MIDI today.

A．personal

B．electronic

C．multimedia

D．network