Which of the following statement is correct?(Here $R=CH_3$)

Question

$\begin{array}{1 1}(a)\;\text{In aqueous solution, }R_2NH(2^oamine)\text{ is a stronger base than } RNH_2(1^oamine)\\(b)\;\text{In aqueous solution, }R_3N(3^oamine)\text{ is a stronger base than } R_2NH(2^oamine)\\(c)\;\text{In aqueous solution }R_3N \text{ is a stronger base than }RNH_2\\(d)\;\text{Above all}\end{array}$