c
\(\begin{array}{l}
For\,swimmer\,to\,cross\,the\,river\,straight\\
\Rightarrow \,\,\,\,\,4\,\sin \,\theta = 2\\
\Rightarrow \,\,\,\,\,\sin \,\theta \, = \frac{1}{2}\, \Rightarrow \,\theta \, = {30^ \circ }\\
So,\,angle\,with\,direction\,of\,river\,flow\,\\
= {90^ \circ } + \theta = {120^ \circ }.
\end{array}\)
