Spurred by the discovery that a substance containing uranium emitted radiation, Marie Curie began studying radioactivity in 1897. ███ █████ ██████ ████ ███ ██████ ███ █████████ ███ █████ █████ ███ ████ ██████ ████████████ █ ███████ ████ ███ █████ ██ ███████ ████████ ███ ██████████ ████ ██ ███ ████ ███████████ ████ ████████ ██████ ██ ███ ██████████ ████ ███████████ ████ ███████ ██ █████ ███ █████ ███████████ ████████ █████ ███ ████ ██ ███████ █ ████ ██ ██████████ ███████ █████████ ████████ ███ ███████ ███████ ███ █████████ ██ ███ ████ ██ ███████████ █████████ ███ ██████████ ████ ███████ ███████ █████████ ██ █ ██████████ █████ ████ ██ ██████ ██ ██████████ █████ ██ █████ ████████ █████ █████████ ████ ███ ████████ ████ ███ █ █████ ███████ ███ █████████ ████████████ ███████ █████████ ████████ ██ ██ ████████████ ████ ██ ███████████ ██████████ ███████ █████████ ███ ████████████ █████████ ███ ███ ██████ ██ █████████ █
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Which one of the following ████ ██████████ █████████ ███ ███████ ██ ███ ████ █
the physical process ████ █████████ █ ██████████
This best captures the meaning of “mechanism” as used in the last sentence of P1. Curie failed to identify the physical process that explains why radiation occurs.
the experimental apparatus ██ █████ █ ██████████ ██████
There’s no reason to think “mechanism” refers to an experimental apparatus. It doesn’t make sense for Curie to have been unable to “postulate” an experimental apparatus. She would have been able to describe the experimental tools she used.
the procedure scientists ███ ██ █████ █████ ███ ██████████ ██ █ ██████████
It doesn’t make sense for Curie to have been unable to “postulate” the procedure she used to bring about radiation. She would have been able to describe her experiment and what she did. What she didn’t understand was the exact physical process that was occurring when an element exhibited radiation.
the isotopes of ██ ███████ ██████ ██ ███████ █ ██████████
Curie didn’t know about isotopes. So it wouldn’t make sense for the author to write that Curie couldn’t “postulate” an isotope to explain radiation. She would have had no reason to think of radiation in terms of isotopes.
the scientific theory ██████████ █ ██████████
The thing Curie was unable to postulate was a causal explanation for why/how radiation occurs. But it’s not clear that she was unable to “describe” radiation. She did describe certain aspects of radiation — she described the rate of emitting radiation and described different levels of radiation in different elements. What was missing was how radiation occurred, not just a description of radiation. In addition, it’s not clear that the causal mechanisms discussed later in the passage (