Final answer:
The correct answer is flowers (d). An aquarium contains water and often has fish swimming in it. Similarly, a vase usually contains water and is commonly used to hold flowers.
Step-by-step explanation:
The correct answer is flowers (d).
An aquarium contains water and often has fish swimming in it. Similarly, a vase usually contains water and is commonly used to hold flowers. Therefore, the relationship between the words 'aquarium: water' and 'vase: water' is that they both involve putting something inside a container.
Option (a) 'fish' is incorrect because fish are specific to aquariums, whereas flowers can be placed in both aquariums and vases.
Option (b) 'glass' is incorrect because although both an aquarium and a vase can be made of glass, the question is asking for the common element that goes inside these containers, which is water.
Option (c) 'rocks' is incorrect because rocks are not usually placed in vases, while flowers are a popular choice for vase decoration.