Step 1: Political context.
Post-Emergency elections (1977) produced a Janata Party victory—the first non-Congress government at the Centre.
Step 2: PM selection.
Morarji Desai became Prime Minister (1977–1979).
Chaudhary Charan Singh became PM later (1979); Jagjivan Ram was a senior leader; Jayaprakash Narayan led the movement but never held the PM’s office.
Step 3: Conclude.
\[
\boxed{\text{Morarji Desai (Option C).}}
\]