What is the correct $IUPAC$ name for $CH_3-CH(CH_3)-CH=CH-CH_2-COOH$?

The $IUPAC$ name of $C_6H_5COCl$ is

The $IUPAC$ name for $CH_3-CH=CH-CH_2-CH(NH_2)-CH_2-COOH$ is

What is the priority order of the groups $-OH, -COOH, -CHO, -OCH_3$ attached to a chiral carbon according to the $Cahn-Ingold-Prelog$ $(CIP)$ sequence rules?

The $IUPAC$ name of $CH_3COOC_2H_5$ will be

Fill in the blanks:
$(1)$ The $IUPAC$ name of $CH_3COCH_2CH_2CH_2COOH$ is .........
$(2)$ The formula of pent$-4-$en$-2-$ol is .........
$(3)$ The $IUPAC$ name of the following structure is ......... and ......... is the main functional group in it.
(Structure: $A$ cyclohexene ring with an $-OH$ group attached to the carbon adjacent to the double bond,such that the double bond is between carbons $2$ and $3$ relative to the $-OH$ at position $1$.)
$(4)$ For $CH_3CH(OH)CH_2CH_2CH_2CHO$,the main functional group and the second priority group are ......... and ......... respectively.