液压系统调速的方法主要有（）。

A、节流调速

B、容积调速

C、容积节流调速

D、回油路节流调速

E、旁油路节流调速

Why is it important to have a project charter ？（）

A．It is the collection of all subsidiary project documents.

B．The project charter is the necessary basis for all work packages to be performed.

C．It formally authorizes the project.

D．It tracks the progress of the project.