Imagine that the arable land is scarce then people will compete for land in competition will be big this means that it is more likely to be able to find smaller pieces of land for it is likely that the size of the House and farms will be small
Answer:
I would go with A. Salinity and Temperature
Drainage basin - the area of land drained by a river.
Catchment area - the area within the drainage basin.
Watershed - the edge of highland surrounding a drainage basin which marks the boundary between two drainage basins.
Source - the beginning or start of a river.
Confluence - the point at which two rivers or streams join.
Tributary - a stream or smaller river which joins a larger stream or river.
Mouth - the point where the river comes to the end, usually when entering a sea.
Hope this helped :)