这篇英语完形填空括号了的mostly能不能替换成obviously

题目

这篇英语完形填空括号了的mostly能不能替换成obviously
答案是mostly,请问怎么判断,这是完型填空选取的原文的片段,完型填空题目有简化.直接搬字典中文意思的勿扰.
When I first started running,it was to lose weight.I dragged myself to the treadmill about once a week,or sometimes just once a month.There was no ‘big goal’,and I was never really that good at it.I got out of breath,my chest hurt,and I made a hundred excuses.It took me a year to run more than three miles.
I wasn’t making much progress,especially weight-wise.( Mostly),it was because I didn’t do it enough.
Then one summer,when the weather was particularly good,I went for a run.Just a gentle jog in the June breeze,and to my surprise,I actually enjoyed it.I ran a couple more times that week,then a few more the week after,and within that month,running turned from a chore to a hobby.
While I was running for superficial reasons (ie.to lose weight) and not making much progress,I would be completely put off by just the number on the scales.I would think,‘What’s the point?‘.But,after th

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