A prepositional phrase is one where a preposition carries an object.
2
动宾词组我们认为下滑原因主要是由于热水器市场同类产品竞争激烈所致。
We attribute the drops to the pressing competition of the heating products market.
3
许多同志省掉了不应当省掉的主词、宾词,或者把副词当动词用,甚至于省掉动词,这些都是不合文法的。
Many comrades tend to omit the subject or the object of a sentence when it should not be omitted or use adverbs as verbs or even leave out verbs. all this is ungrammatical.