This is a photo that I took 5 years ago from a moving train going thru Osaka.('thru' is a slang abbreviation for 'through'.)
I think that the curved thing is a roller coaster track.
A 'roller coaster' is a ride where people sit in small open train cars and go and down.
If you say that something is a roller coaster, you mean that there are many violent ups and downs.
For example: my life is a roller coaster.
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There is a flu going around today. I might be getting sick.
