Identify `(A)` to `(D)`.
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Explanation

proceed reverse retrosynthetic analysis from `(D)`. First, find the structures of `(D)` and `( C)`.
`DU "in" (D) = ((2n_C +2)N=n_H)/(2) = ((2 xx 3 + 2)-6)/(2) = 1^@`
One `DU` in `(D)` with one oxygen shows that `(D)` can be aldehyde or ketone with three `C` atoms. It cannot be aldehyde, because on oxidative ozonolysis `(O_3//H_2 O)`, aldehyde is never obtained. it is because the aldehydes are converted to acids on oxidative ozonolysis.
Therefore, `(D)` is acetone (a ketone)
Number of `C` atoms in `( C) = 6`
So, `2 mol` of acetone is produced from `(C )`.
Therefore, structure of `( C)` is as follows :

`( C)` is obtained by the dehydration of `(B)`. Therefore, `(B)` is a `3^@` alcohol. The structure of `(B)` is `(B)` is obtained by the reaction of ester with `CH_3 MgBr`. Ester on reaction with `G.R` gives `3^@` alcohol, with two `R` groups `(R = -Me)` coming from `G.R` and one `R'` group from ester
So, the structure of `(A)` is OR". The value of `R"` in ester can be either group or group, since the total number of `C` atoms in `(A)` is `7`.
The number of `C` in group `= 4`.
So, the total number of `C` atoms in `R"` should be `(7-4) = 3` Three `C` atoms alkyl group can be either isopropyl or propyl. Reaction are as follows :