Besides sounds and phonetic symbols, the teaching of pronunciation also includes other aspects, such as stress, （）, and rhythm.

A.You know you can’t afford it all.

B.How’s your first month at college？

C.Wow, where did your money go？

D.I promise I’ll return it.

A.[m]

B.[f]

C.[p]

D.[b]

A.You know you can’t afford it all.

B.How’s your first month at college？

C.Wow, where did your money go？

D.I promise I’ll return it.

A.[m]

B.[v]

C.[p]

D.[b]

which of the following sounds is a voiceless bilabial stop？

A.[p]

B.[m]

C.[b]

D.[t]

A.[b]

B.[d]

C.[p]

D.[k]

A./t/

B./g/

C./p/

D./k/

The four sounds /p/, /b/, /m/, /w/ have one feature in common, i.e. they are all

A．bilabials.

B．labiodentals.

C．fricatives.

D．dentals.

landing in dense fog, a pilot must use radar, an alternative way of navigating. Since human eyes are not very good at determining speeds of approaching objects, radar can show a pilot how fast nearby planes are moving. The basic principle of radar is exemplified by what happens when one shouts in a cave. The echo of the sounds against the walls helps a person determine the size of the cave. With radar, however, the waves are radio waves instead of sound waves. Radio waves travel at the speed of light, about 300, 000 kilometers in one second. A radar set sends out a short burst of radio waves: Then it receives the echoes produced when the waves bounce off objects. By determining the time it takes for the echoes to return to the radar set, a trained technician can determine the distance between the radar set and other objects. The word "radar," in fact, gets its name from the term "radio detection and ranging." "Ranging" is the term for detection of the distance between an object and the radar set. Besides being of critical importance to pilots, radar is essential for air traffic control, tracking ships at sea, and for tracking weather systems and storms.

What is the main topic of this passage？

A．The nature of radar.

B．Types of ranging.

C．Alternatives to radars.

D．History of radar.