How many distinct resonances would appear in the (proton-decoupled) ¹³C NMR spectrum of 1,1-diethyl-3-methylcyclobutane?

Question

Quizplus · Accepted Answer

1,1-diethyl-3-methylcyclobutane has 6 unique carbon atoms, thus it could have a maximum of 6 distinct resonances in its NMR spectrum. However, some of these carbons may be overlapping due to their similar chemical environments. 
Looking at the molecule, we can see that the two methyl (CH3) groups are chemically equivalent and will produce a single resonance at the same chemical shift. Thus, we can treat them as a single carbon. Similarly, the two ethyl (CH2CH3) groups are also chemically equivalent and will produce a single resonance at the same chemical shift, so we can treat them as a single carbon too. 
Therefore, the molecule can be simplified into a system of four distinct carbon atoms, which would give rise to a maximum of 4 distinct resonances in the NMR spectrum. Thus, the answer is C) 6 distinct resonances.

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How Many Distinct Resonances Would Appear in the (Proton-Decoupled) ¹³C