= Solution
There are three stretching fundamentals, although four stretching-region features are listed. The low feature at $1746\ \mathrm{cm^{-1}}$ is predominantly C=O stretch ($A_1$). The two features at $2783$ and $2843\ \mathrm{cm^{-1}}$ are the symmetric and antisymmetric C–H stretches; their order is not determined by this mode count alone.
The $3482\ \mathrm{cm^{-1}}$ feature is consistent with the first C=O <vibrational overtone>, close to $2(1746)=3492\ \mathrm{cm^{-1}}$ and shifted downward by <anharmonicity>. Its symmetry is $A_1\otimes A_1=A_1$, so symmetry permits the weak anharmonic transition. It is not a fourth stretching fundamental. The combination-band evidence in the next part distinguishes the two C–H assignments.
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