The answer to this question is Voluntary.
One negative aspect about the voluntary aspects of research is that it may damage the validity of the research.
For example, if research is being done through questions about certain topics. People who know the purpose of the research could fake the data to obtain positive results.
What wave?.... we need the full question
The Pony express was affected by mechanization because the Pacific Telegraph line had replaced the pony express route which also helped deliver mail faster, safer, and easier. The pony express founders were now losing money due to lack of business and went bankrupt.
Taxes and spending is correct i believe
Answer: An elected congress will be too weak to balance out the power of the president.
Explanation: The other answer choices are not true