i study by having conversations with friends在线等!为什么have要变having

问题描述:

i study by having conversations with friends在线等!
为什么have要变having

by 是介词,后加名词或动名词
He saluted her by raising his hat.
他举起帽子向她致意.
They sold apples by catty.
他们按斤卖苹果.