Question 22: Read the passage and choose the best option to complete each blank. Any change in one part of an ecosystem can cause changes in other parts. Droughts, storms and fires can change. Some changes ____46___ systems. If there is too little rainfall, plants will not have enough water to live. If a kind of plant dies off, the animals____47___feed on it may also die or move away. Some changes are good for schools. Some pine forests need fires for the pine trees to reproduce. The seeds are sealed inside pinecones. Heat from a forest fire melts the seal and lets the seeds ____48___. Polluting the air, soil, and water can harm systems. Building dams on rivers for electric power and irrigation can harm harmonize ____49___ the rivers. Bulldozing wetlands and cutting down forests destroy systems. Ecologists are working with companies and governments to find better ways of ___50____ fish, cutting down trees, and building dams. They are looking for ways to get food, lumber, and other products for people without causing harm to learning (48)……….
Let something out: to let something fall out.
The previous sentence said that the seeds are in the pinecore, so when burned, the seeds will fall out and grow into a tree.