英文問題請教aaaa?

An enchancement added to the value Simon:-
The major economic reforms "introduced by China 40 yrs ago" "where(interr.adv) hundreds of millions of people"-----------------S
have been lifted (=having lifted=Participial perfect)-------V
out of poverty
and---------conjunction connecting two clauses
has been leading China to becoming---------(=having led is Participial perfect+gerund)(Participial present+ gerund accompanying)--------V
the 2nd largest
(totalitarian system economies=entity real existence=economy)
in the world.------------------------------------------------------------------------O

lead to = 導致...後果, 結果 (a phrasal verb, transitive)

The participle construction used above has a cause-and-effect relationship (adverbial) with the main clause.
The construction is comprised of TWO participle phrases joined together by the conjunction "and".
In other word, the second participle "leading" cannot be changed to "lead" (either a bared infinitive or a finite verb of present tense)

"it (or should be "its" in formal English) becoming the second-largest ...", the object of phrasal verb "lead to", is a possessive gerund phrase with "it" referring to "China". For the same reason, the verb "become" has to be in non-finite form of gerund and can't be changed to "become".

However, If it needs to be rewritten, I would use adverb clause.
(the subject of the participle construction is not "Economic reforms in China", and the sentence is not a reduction of relative clause; otherwise, a comma should have been used instead of a dash which is used to provide additional or summarized information, with a surprising effect.)

As a result of the major economic reforms introduced by China forty years ago, hundreds of millions of people (in China) have been lifted out of poverty and China has become the second-largest economy in the world.

不行
Forty years ago, China introduced major economic reforms – lifting (lifting 的累贅寫法為economic reforms in China lifted) hundreds of millions of people out of poverty and leading (leading 的累贅寫法為 major economic reforms in China led ) to it becoming the second-largest economy in the world.
分詞構句為很好的用法，如要用很累贅的寫法就應將主詞(economic reforms in China)寫出，其動詞配合句意為過去式(led，不是lead)，且and的兩邊寫法也應一致

Forty years ago, China introduced major economic reforms.
Economic reforms in China lifted hundreds of millions of people out of poverty and (economic reforms in China 相同主詞宜省略) led to it becoming the second-largest economy in the world.
==>
Forty years ago, China introduced major economic reforms.
Economic reforms in China lifted hundreds of millions of people out of poverty and led to it becoming the second-largest economy in the world.