The government agency requires all applicants to fill out duplicate
forms when filling a grant request and to put their social
security number on every form.
想要请问一下这边的When是什么词性?
问了一位是说When当介系词后面加Ving
如果When当连接词后面接S加上V
另外一位的说法是说When通常是不能拿来当介系词
说这边的when是连接词后面的filling是分词构句??
两位不同的说法???哪一方说法才是正确的~跪求文法达人