D) Scientific laws do not account for unseen variations, like wind
Explanation:
Will model in predicting the path of an arrow he was about to shoot failed because scientific laws most times do not account for unseen variations like wind.
Scientific laws are the description of an observed phenomenon in nature.
- Most scientific laws have exceptions.
- Exceptions in scientific laws are conditions in which the law will not hold true.
- There are exceptions to newton's law of motion which Will did not take into account.
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Newton's law brainly.com/question/11411375
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Before getting an answer for it first we have to understand nuclear fusion.
Nuclear fusion is a thermo-nuclear reaction in which two light unstable nuclei will form a heavy stable nuclei. In this process there will be some mass defect which will be converted into energy as per Einstein's mass energy equivalence theorem.
The theorem is stated as
where c is the velocity of light and m is the mass converted into energy.
One take an example of fusion in sun where 4 hydrogen atoms combine to form a helium nucleus which are explained below-



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Here
is the positron.
In this process very high temperature is needed which is approximately equal to the temperature of the sun i.e 
Such temperature is very difficult to initiate the reaction on the earth surface. It should be carried out in an sustainable way also .Otherwise It will cause nuclear hazards.
If you have (1 x 10⁹) cubic meters of volume, and 1/2 gram of mass
in each cubic meter, then you have
(1/2 x 10⁹) grams = (5 x 10⁸) grams = (5 x 10⁵) kilograms of mass .
On Earth, that mass weighs 4,900,000 newtons .
(about 1,102,300 pounds)
(about 551 tons)