Answer:
D. S and X
Step-by-step explanation:
The pair that is at the same level of structural organization is S and X.
S is the brain of human
X is the leaf of plant.
Both the brain and the leaf are in the organ level of organization. The brain is an organ in human body which carries out most activities in the body. It controls all functions of the body and also interprets information from the outside world. The brain is the seat of intelligence, emotion, creativity and memory.
The leaf in plants is a collection of tissues. It enables photosynthesis to occur. The leaf traps sunlight and carbon dioxide which are used during photosynthesis to manufacture food for plants.