An ephemeral stream gets most of its water from
a oceans
b other streams
c rain
d floods

I think the answer should be: c rain 
The ephemeral stream does not flow all around the year. The stream is located above the water table so normally there is no water there. This kind of stream mostly found in low rain area. Water will flow if the stream if there is a rain pouring the land above. In dry season, the stream would not have any water.