What is the level of classification where two organism are the most similar but not the same species?

i think it will be the gender

Explanation:

example: we have brown and white and black men

they all in the same spieces ( masculine human) but with different genders

the answer is either b or c

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.