It takes a noun and a verb to make a complete sentence.
There isn't a single verb in a), b), or c).
"Affords" is the verb (predicate) in d)., the only complete sentence.
They share covalent bonds
Answer:
A works to find magnitude. The leading negative sign gives us the positive magnitude after the correct velocity is found without it.
Answer:

Explanation:
Given:
mass of ice melted, 
time taken by the ice to melt, 
latent heat of the ice, 
Now the heat rejected by the Carnot engine:



Since we have boiling water as hot reservoir so:

The cold reservoir is ice, so:

Now the efficiency:



Now form the law of energy conservation:
Heat supplied:

where:
heat supplied to the engine




Now the work done:


