Classify each statement below as an observation or as an inference based on the current Big Bang model. $($Note that the helium abundance is defined as the mass of helium relative to the mass of hydrogen.$)$

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The cosmic microwave background is radiation left over from the Big Bang.

Large$-$scale structure looks about the same in all directions.

The temperature of the cosmic microwave background varies slightly with direction.

Fusion during the universe's first five minutes produced $\backslash (75\backslash \%\backslash )$ hydrogen and $\backslash (25\backslash \%\backslash )$ helium $($by mass$).$

Photons of the cosmic microwave background have traveled through space for almost $14$ billion years.

The helium abundance is at least

Large$-$scale structure grew around $\backslash (25\backslash \%\backslash )$ in every galaxy studied so far. density variations present in the early universe.