What is the common name of $2, 3$-dihydroxybutanedioic acid?

What is the $IUPAC$ name of the following compound?
$CH_3-CH_2-C(Br)=C(CH_3)-CH_2-CH_3$

What is the $IUPAC$ name of the following compound?
$\begin{array}{c} H \\ | \\ CH_3-C=C-CH_3 \\ | \\ CH_2CH_3 \end{array}$

The $IUPAC$ name of $CH_3-CH_2-C(CH_2CH_3)_2-CH(CH_3)-CH_2-CH_2-CH_2-CH_3$ is

The $IUPAC$ name of the compound $CH_3-CH=CH-CH=CH-C \equiv C-CH_3$ is:

Which of the following $IUPAC$ names is correct for the structure:
$CH_3-CH(CH_3)-CH_2-CH_2-CH_2-CH(CH_2-CH_2-CH_3)-CH_2-CH_3$?
$(i)$ $2-$methyl$-6-$ethylnonane
$(ii)$ $6-$ethyl$-2-$methylnonane
$(iii)$ $4-$ethyl$-8-$methylnonane