The answer is a) fresh. Most lakes contain freshwater, which means the water has low concentrations of salts. This is primarily due to the fact that they are fed by rivers, streams, and precipitation which do not contain significant salt content.
However, there are exceptions, such as saltwater lakes or saline lakes like the Great Salt Lake in Utah or the Caspian Sea, which is technically a lake despite its saltiness. But in general terms, if you consider the majority of lakes around the world, they primarily hold freshwater. So, lakes can predominantly be classified as having fresh water.