The correct option is B increase
One of the major functions of every ecosystem is decomposition.
The process of decomposition is the breakdown of complex organic materials present in dead remains of plants and animals (detritus) into simple inorganic compounds.
The rate at which decomposition occurs is dependent on multiple factors such as chemical composition of the detritus, environmental temperature and soil moisture.
A warm temperature favours the rate of decomposition whereas low temperatures slow down the rate of decomposition. The rate of decomposition is higher when the soil is moist.
Hence, when the temperature is warm and the soil is moist, the rate of decomposition will increase.