$(a)$ How does the construction of dams across rivers get linked with the production of greenhouse gases?
$(b)$ How do technological inputs improve the efficiency of biomass fuels?

(N/A) When dams are constructed,large areas of vegetation are submerged. This submerged vegetation rots under anaerobic conditions,leading to the production of large amounts of methane,which is a potent greenhouse gas.
$(b)$ Technological inputs improve the efficiency of biomass fuels in the following ways:
$(i)$ Conversion of biomass into biogas in a biogas plant,which is a cleaner and more efficient fuel.
$(ii)$ Conversion of wood into charcoal by heating it in a limited supply of air (pyrolysis). Charcoal has a higher calorific value,burns without smoke,and is a more efficient fuel compared to raw wood.