The third answer is the one you want. You have to have an adjustable density. All other things being equal, if the tanks you use for holding just water when filled with water will let the sub sink, because the sub is made of a dense metal like iron or steel.
If on the other hand you fill these tanks with air, the net density will be below one and the sub will rise.
D.) It cannot be broken down into a simple substance through chemical means...
CO2<span> is a linear molecule and the Oxygen (O) atoms on each end are symmetrical. Polarity results from an unequal sharing of valence electrons. Because of this symmetry there is no region of unequal sharing and </span>CO2<span> is a</span>nonpolar<span> molecule</span>
<h2>Answer:</h2>
Compound. Option A is correct
<h2>Explanations:</h2>
When two or more different elements combines, a compound is formed. For instance, if carbon and oxygen combines, carbondioxide is formed according to the equation;

From the reaction, carbon and oxygen are the elements while carbondioxide is the compound. Hence we can conclude that a pure substance formed when two or more different elements combine called compound.