Explanation

(c)
The basic character of amines depends upon the capacity nitrogen atom to donate an electron pair. More the ability of nitrogen atom to donate electron pair, more will be the basic character. In presence of electron releasing groups (+I showing group, $- CH_{3}$) the basic character of amines increases due to more availability of electrons on nitrogen atom.
Tertiary amines are least basic due to steric hindrance caused by three bulky alkyl groups.
$\therefore$The order of basic character is
$NH\left( CH_{3} \right)_{2}$ > $CH_{3}NH_{2}$ > $N\left( CH_{3} \right)_{3}$ > $NH_{3}$