Trilobites are index fossils because they a. changed slowly through time c. exhibit specific characteristics b. lived over large areas of the world d. all of the above select the best answer from the choices provided a b c d

Answer: Option D all of the above

Explanation:

Index fossils are the ones which are used to define as well as identify geological periods.Trilobites are one of the earliest known groups of arthropods.There are thousands of species of trilobites that are known and they are found in various parts of the world. The main reasons that trilobites are considered as index fossils because they were found to live in many regions of the world during specific period in the geologic time.They first appeared in the early Cambian period and then increased in number through the Palaeozoic era and finally disappeared at the end of the permian.Trilobites appeared quickly in the geologic time and then moulted just like the other arthropods and thus, are used as index fossils by scientists.

Thus, all the characteristics mentioned in the options are the reasons why trilobites are used as index fossils.

The fear of communism in the United States was fueled by Senator Joseph McCarthy and the proceedings of the  House Un-American Activities Committee.

Joseph McCarthy was a US Senator that claimed to have a list of communists that were involved in the US State Department in the 1950's. The shock of this accusation made American citizens more paranoid about the government. Along with this, McCarthy began accusing other politicians, celebrities, and even the US military of having communist influences.

This rise in McCarthyism helped increase the amount of proceedings in the House Un-American Activities Committee (HUAC). HUAC was run by the US Congress. Congress would call in citizens to question their ties to communism or the Soviet Union. These hearings ruined the lives of hundreds of American citizens and only caused more paranoia among US citizens after seeing them on TV.