Organic chemistry

here it asks for the aldehyde so the answer is C I guess but I get confused with the explanation in the bracets

The explanation in the bracket with the Asterisk mark is for the Ether as we know that Ethers are represented by R-o-R* what they mean by R* is that it can be different from the other R broadly speaking Ethers are classified under symmetrical (i.e having same R groups) and asymmetrical having different R groups so for eg: one R can be -CH3 while the other be -C2H5 so they are different this is what they are conveying here.
Hope it helps!