这一题 on 后面为什么用that on that foggy a day

问题描述:

这一题 on 后面为什么用that on that foggy a day
26.Polly’s mother was anxious about ______ she could get home safely on ______ foggy a day.
A.whether; that B.if; that C.whether; such D.if; so

A谢谢,能解释一下on that foggy a day 中that 的用法吗副词 ad. 1.【口】那样,那么Is the problem that easy? 问题有那么简单吗?