"since 1923, the united states flag code has provided advisory rules for displaying and handling the us flag." what kind of sentence is this

5. the following question refers to the four selections by albert einstein: these readings show that, between 1939 and 1952, einstein a) abandoned science and turned to political activism. b) revised his opinions about the need for nuclear weapons. c) worked tirelessly to abolish nuclear weapons. d) devoted himself solely to scientific research.