Which of the following statements is true when using acetylene flame atomization in atomic absorption spectrometer

A、Whenigniting,airshouldbeintroducedfirst,thenacetylene;
B、Whenigniting,acetyleneisintroducedfirst,thenair;
C、Whenflameout,turnofftheairfirstandthenacetylene;
D、Noneoftheaboveistrue