Answer:
C
Explanation:
A theory can be changed when new evidence is found. A law doesn't change because it is universally a fact. It doesn't need new evidence to support it.
Answer:
c. 3/2 mg
Explanation:
Given that the acceleration of an elevator is 1/2 g upward.
The reading on the scale of the elevator is the net external force acting on the elevator.
Let the force F acting on the elevator as shown,
By using Newton's 2nd law, 
where,
is the net force acting on the elevator.
m is the mass of the elevator,
a is the acceleration of the elevator, as given a=1/2 g upward.
So, 

So, the reading on the scale in the elevator is
.
Hence, option (c) is correct.
Answer: 
Explanation:
If we have an initial amount of a radioactive material or substance, which is
, and we also are told this amount decays
each year, this means each year
of the substance remains:

<u />
<u>To understand it better:</u>
Year 1: 
Year 2: 
Year 3: 
and so on until year
:
Year t: 
Therefore, the function tha best describes this radiation decay situation is:

Mass of oxygen stays the same.