Which of these events happened in the 20th century? a)tutankhamen becomes the leader of egypt. b) bartholomew diaz lands on the cape of good hope. c)nelson mandela becomes the president of south africa. d) they pyramids are built along the nile river in egypt.

I believe the correct answer is: C) Nelson Mandela becomes the President of South Africa.

     The only event in this question that happened in (the end) 20th century is that Nelson Rolihlahla Mandela, a South African revolutionary, political leader, and philanthropist, became President of South Africa in 1994, and served as President to 1999.

     Tutankhamun ruled in Egypt from 1332 to 1323 BC, the pyramid were constructed from 2630 BC to 2611 BC and Bartolomeu Dias landed on the Cape of Good Home in 1488.

this null effect is caused by a weak manipulation and ineffective internal validity. in a scientific study, as the one dr. morimoto is trying to perfom, internal validity refers to the confidence placed in the cause-effect relationship and to how well an experiment is done and able to eliminate confounding variables.