Cnidaria and flatworms exchange gases and remove wastes by way of their:
A) open circulatory systems. B) closed circulatory systems. C) gastrovascular cavities. D) moist skin surfaces. E) respiratory and excretory systems.

List the advantages and disadavantages of the switch from persistent chlorinated hydrocarbon pesticides (such as ddt) to nonpersistent organophosphate pesicides. have the benefits of the switch outweighed the disadvantages? explain.

Which statements describe resources? one of the factors people use when deciding where they will live is the availability of resources. renewable resources have little value for people. resources are unevenly distributed throughout the world. energy is the world resource which has the highest use. the use of nonrenewable resources has decreased in recent history. the use of resources is evenly distributed throughout the world. the world's oil supply will last for the next forty years if its use continues as expected.

The negative impacts of nonnative species generally outweigh the positive impacts