In modern fathometers the sonic or ultrasonic sound waves are produced electrically by means of a(n)（）.

“Full speed ahead” and “Full speed astern” are（）given by the officers or the pilots.

Camshafts are usually driven by timing gears or （）.

把课程理论与教学理论放在平列的水平来看，课程论研究的是教学什么，教学论侧重研究的则是怎样教学。

从学科发展渊源来说，大学教学论是教学论在高等教育领域的延伸和拓展，是教学论学科新近开辟的研究领域。

The symbol (GB786√1-93) at right side represents （）

（）are represented by phonetic symbols because there is no one-to-one correspondence between written letters and spoken sounds.

Let @ represent one of the four basic arithmetic operations such that, for any nonzero real numbers P and Q, P @ 0=P and P @ Q=Q @ P. Which arithmetic operation(S) does the symbol @ represent?

Sometimes lights are（）by fog，haze，dust，smoke，or precipitation which may be present at the light，or between the light and the observer，and which is possibly unknown by the observer.

The floors in a vessel’s hull structure are kept from tripping，or folding over，by（）.

The legend/symbol which designates an occluded front is represented by a（）.