Experiment comparing the effect of fertilizer on flowering plant growth.

Let me work through this problem step by step.

Question 1: Which question is being tested?

Looking at the diagram:
- Both plants receive 200 mL of water
- One plant gets fertilizer (shown with "10 mL fertilizer" being added)
- The other plant does NOT get fertilizer (only water)
- Everything else appears to be the same (same size pots, same type of plants)

This is testing whether adding fertilizer makes a difference in how the plants grow.

Let me check each option:
- a. "Do flowering plants grow taller when watered with salt water?" - No, there's no salt water mentioned
- b. "How much fertilizer do flowering plants need?" - No, they're not testing different amounts
- c. "Does adding fertilizer cause flowering plants to grow taller?" - Yes! This matches what's being tested
- d. "What is the best kind of fertilizer?" - No, they're only using one type

Answer for Question 1: c

Question 2: Identifying variables

In an experiment:
- Change variable (also called independent variable): What you change on purpose
- Responding variable (also called dependent variable): What changes as a result
- Control variables: Things you keep the same

Looking at the labels:
- a. "the size of the pot" - This should stay the same for both plants, so it's a CONTROL variable
- b. "the kind of potting soil" - This should also stay the same for both plants, so it's a CONTROL variable

Wait, let me reconsider. The question asks to write which type of variable each item is. But looking at the blank lines, I think they want me to identify what these are in THIS specific experiment.

Actually, re-reading more carefully: The blanks appear to be asking what TYPE of variable each labeled item is. Both "the size of the pot" and "the kind of potting soil" are things that should be kept constant (controlled) in this experiment, so both are control variables.

However, I notice the formatting shows two separate items (a and b), and the instruction says to write the appropriate term beside each. Let me verify my understanding once more.

For this fertilizer experiment:
- Change/independent variable: Whether or not fertilizer is added
- Responding/dependent variable: How tall the plants grow (or their growth)
- Control variables: Pot size, soil type, amount of water, type of plant, etc.

So:
- a. the size of the pot = control
- b. the kind of potting soil = control

Both of these are control variables because they need to be kept the same for both plants to make it a fair test.

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Final Answer:
1. c
2. a. control
b. control