I started to write my own original sentences using the grammar I was learning.这个句子中using前是不是省略了一个byI was 前是不是省略了一个that?by+doing 中的by能省吗省略的怎会是that was?"that"代指什么？

I started to write a letter.同义句 I started to write a letter.同义句 翻译;I started to write my own original sentences using the grammar I was learning 翻译这个句子；Then I started to write my own original sentences using the grammar I was learning. then I started to write my own original sentences using the grammer i was learning谁帮忙翻译一下这 (人工翻译）then i started to write my own orginal sentences using the grammar i was learning. ____ the paper,i have to write it carefullya:starting b:after startingc:having started d:once i start i started to write my own original sentences using the grammar i was learning.中的use为啥加ing? I‘m very glad to write to you. I started to miss you. I'm here in England____ (write) to you.writing 还是to write 详解.VERY THANKS . .---Please write down the sentences.---I’m sorry I don’t...writing C.for write D.to write with I’m too busy_______(write）to my parents often i'm feeling better,so i've started _______.是taking lessons还是to take lessons I'm sorry,I'm too busy ______to you A.writing B.to writing C.with write D.to write When I got home,I started to think about (what) to write my father is an astronaut为什么填what不填how i'm sorry (to hear)that为什么填to hearwill you promise(to write) to me为什么填to write Then I started to write my own original sentences using the grammar I was learning.using做状语 为什么用过去分词形式