Question

two fish tanks with elodea
two red lights
two green lights
four goldfish
using only these supplies, which questions can keenan investigate with an experimen
select all that apply.
does elodea release more oxygen when kept in a tank with a red light or a
tank with a green light?
does elodea release more oxygen when kept in a tank with four goldfish
or a tank with four guppies?
does elodea release more oxygen when kept in a tank with four goldfish
or a tank with six goldfish?
does elodea release more oxygen when kept in a tank with a red light or a
tank with a blue light?

Explanation:

To determine which questions can be investigated, we check if the supplies are available:

• For "Does elodea release more oxygen when kept in a tank with a red light or a tank with a green light?", we have red lights, green lights, and elodea - supplies exist.
• For "Does elodea release more oxygen when kept in a tank with four goldfish or a tank with four guppies?", guppies are not among the supplies (only goldfish are given), so this can't be investigated.
• For "Does elodea release more oxygen when kept in a tank with four goldfish or a tank with six goldfish?", we only have four goldfish, so six goldfish are not available - can't be investigated.
• For "Does elodea release more oxygen when kept in a tank with a red light or a tank with a blue light?", blue lights are not among the supplies (only red and green lights are given) - can't be investigated. Wait, but the original check in the image might have errors. Wait, re - evaluating: The first question has red and green lights (supplies: two red, two green, elodea, tanks). So the first question is valid. The second question: guppies not available. Third: six goldfish not available. Fourth: blue light not available. So only the first question is valid. But the original image had some checked, but based on supplies:

Supplies: two fish tanks with elodea, two red lights, two green lights, four goldfish.

1. "Does elodea release more oxygen when kept in a tank with a red light or a tank with a green light?": We have red lights, green lights, elodea, tanks. So this is possible.
2. "Does elodea release more oxygen when kept in a tank with four goldfish or a tank with four guppies?": Guppies are not provided, so no.
3. "Does elodea release more oxygen when kept in a tank with four goldfish or a tank with six goldfish?": We only have four goldfish, so six are not available, no.
4. "Does elodea release more oxygen when kept in a tank with a red light or a tank with a blue light?": Blue lights are not provided, so no.

So the only valid question is "Does elodea release more oxygen when kept in a tank with a red light or a tank with a green light?".

Answer:

The valid question is: Does elodea release more oxygen when kept in a tank with a red light or a tank with a green light? (The other options are invalid as they require supplies not available: guppies, six goldfish, blue light).