Identify the total number of substituents present in the given compound.

The $IUPAC$ name of $CH_3-CH(OCH_3)-CHO$ is

What is the $IUPAC$ name of the compound $CH_3-CO-CH_2-CH(OH)-CHO$?

Give the correct $IUPAC$ name for the following structure:

Given below are two statements:
Statement $I$: $IUPAC$ name of $HO-CH_2-(CH_2)_3-CH_2-COCH_3$ is $7-$hydroxyheptan$-2-$one.
Statement $II$: $2-$oxoheptan$-7-$ol is the correct $IUPAC$ name for above compound.
In the light of the above statements,choose the most appropriate answer from the options given below:

Provide the $IUPAC$ name for the compound: $CH_3-CH(COOH)-CH_2-CH(COOH)-CH(CH_3)-COOH$.