Whats is correct definition of urban center

Articles of the confederation is a good representation of a system of government.

According to subpart d, research with children may be eligible for exemption when: the children will be asked to complete a surveythe research involves the use of educational teststhe children will be interviewed by the researcher.the research with children will involve participant observation with researcher interaction.

Science cannot describe things that a.) are beyond imagination, experience, or human ability b.) cannot be observed, measured, or tested c.) have not been conclusively proven d.) occur without being seen, heard, or felt