大气污染物是指由于人类活动或自然过程引起某些物质进入大气中，并对人和环境产生有害影响的物质。

此题为判断题(对，错)。

此题为判断题(对，错)。

下列说法正确的是(  )。

A．大气污染仅由人类行为引起

B．大气污染既可以由人类行为引起也可由自然活动引起

C．人为活动引起的大气污染包括生活污染、工业污染和交通污染

D．法律所要防治的污染主要由人为活动引起

The need for public speaking is only for national leaders and great people.

The greatest thinkers, scientist, and inventors have often taken information that was readily available and put it together differently to produce new insight. That is critical thinking.

Articulation and pronunciation are identical.

Stage fright is a common occurrence that some of the greatest public speakers in history have suffered from it.

Vocal variety are the changes in a speaker’s rate, pitch, and volume that give the voice interest and expressiveness.

Distracting mannerism and verbal habits are acceptable in public speaking.