it was 改成 they were
代指two extra steps,当然是复数
当然也可以在learn后面加上them,这样it可视为形式主语
I 改成 me
介词between后面加宾语,所以代词用宾格形式me,而不是主格形式I.
The manufacturing process was greatly improved by adding two extra steps,though it was hard to learn.
The discussion between the supervisor and I was brief and discreet.