The electrons lost from the reaction center of photosystem i are replaced by electrons from

The electron lost from the reaction center of photo system l are replaced by electron form water. 
There are two photosystems in the photosynthesis process and they occur during the light reaction. Photosystem l refers to the second system in the photosynthetic light reaction of plant. When photosystem ll absorbs light, electrons in the reaction-center chlorophyll become excited and they move to a higher energy level where they are trapped by the primary electron acceptors. These electrons that are trapped are then replaced by electrons from water.

The metal is named first

Combustion is the act or process of burning. therefore, i believe the answer is  a: burning wood.