Plzz answer this

i know the answer is d and i can see why can't it also be option a ? ?

Zoe is investigating the composition of substance a, an unknown substance. using chemical processes, she analyzes substance a and determines it is composed of sodium, oxygen, and hydrogen atoms in a ratio of 1 : 1 : 1. what is substance a? a. a compound b. an element c. a heterogeneous mixture d. a homogeneous mixture

What is the independent variable in this investigation? mass volume sample number substance density

Part 1: include important facts found through your research. part 2: include your visual display. include your summary of “the chemistry of water” from the national science foundation website. include your experiment. part 3: include responses to the reflection questions.