下列物 质中，所有原子一定都在同一平面的是（   ）

A．丙烯

B．苯乙烯

C．乙炔

D．氯乙烷

DOM is a platform-and language- (41) API that allows programs and scripts to dynamically access and update the content, structure and style of WWW documents (currently, definitions for HTML and XML documents are part of the specification). The document can be further processed and the results of that processing can be incorporated back into the presented (42) . DOM is a (43) -based API to documents, which requires the whole document to be represented in (44) while processing it. A simpler alternative to DOM is the event -based SAX, which can be used to process very large. (45) documents that do not fit info the memory available for processing.

（43）是（）

A.table

B.tree

C.control

D.event