这篇英语完形填空括号了的mostly能不能替换成obviously

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 that month,I started to truly appreciate running as something fun and healthy to do,not just as a means to an end.
healthier became a part of my daily life,rather than something I begrudgingly tried to fit into it.

这里的意思是绝大部分原因是什么,而不是显而易见是什么,因为当中还可能存在其他原因哈,不能那么绝对,希望帮到你啦,望采纳哈,又不懂可以继续问
再问： 觉得OBVIOUSLY也说的通，很明显，我做的不够。
再答： 完形填空是选最佳答案，有时候说得通的可能有几个，这里绝大部分原因显然更通顺一点，一般中国的考试当中都不要选绝对的那个答案哈