Step 1: Understanding the nuclear diagram.
The nucleus contains a dense, spherical body called the nucleolus and a network of thread-like structures known as chromatin.
Step 2: Identification of label A.
Label A points to a dark, rounded structure inside the nucleus, which represents the nucleolus, responsible for ribosomal RNA synthesis.
Step 3: Identification of label B.
Label B points to the thread-like network spread throughout the nucleus, which is the chromatin network containing DNA and proteins.
Step 4: Conclusion.
Therefore, A is nucleolus and B is chromatin network.