What was one important discovery that the Curies made? O A material's radioactivity cannot be changed by altering the material physically
O A material's radioactivity can be weakened or intensified by changing it chemically.
O Radioactive materials generally contain radium or polonium.
O Radioactive materials are found only in the form of salts.

C is the answer to your question

for step 7 table c on the lab "newtons law of action"   the average time it took the car to travel .25 meters   was 1.92 seconds.

the average time it took the car to travel 0.50 meters was 2.61 seconds

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c-14 is carbon-14, or radiocarbon.   it is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons.