过去五年北京已牵头制定国际标准超500项

This pattern means to obtain information from a source, often a meeting, report, forum, or event. “从” marks the source, and “了解到” means “learned/was informed that.” It is common in formal news style.

This structure gives a time range meaning “in the past five years.” It is used to summarize actions, changes, or achievements over a period up to the present.

“已” is a formal written equivalent of “已经,” meaning “already.” It shows that an action or achievement has been completed or reached by now. It is very common in headlines and official reports.

This pattern means that something ranks first in a certain group or area. “居” is a formal verb meaning “to rank” or “to be in a position.” It often appears in formal and statistical writing.

This is a passive structure using “被,” meaning that something is changed or converted into something else. “转化为” means “to transform into” or “to be turned into.” It is common in formal, academic, and policy language.