Morula is a developmental stage which occurs:

Correct Answer: B

Rationale: The correct answer is B because the morula is a stage between the zygote (fertilized egg) and blastocyst (hollow ball of cells). After fertilization, the zygote undergoes multiple rounds of cell division to form a compact cluster of cells known as the morula. This stage precedes the blastocyst stage where the cells differentiate and form an inner cell mass and outer trophoblast layer. A) After implantation is incorrect because the morula forms before implantation. C) Between the blastocyst and gastrula is incorrect as the morula occurs before the blastocyst stage. D) Between implantation and parturition is incorrect as the morula stage occurs much earlier in development.

Correct Answer: C

Rationale: The correct answer is C: 7. The cervical spine consists of 7 vertebrae, labeled as C1 to C7. Each vertebra plays a vital role in supporting the head and facilitating neck movement. C1 is known as the atlas, C2 is the axis, and C3 to C7 are structurally similar cervical vertebrae. These vertebrae house the spinal cord and provide flexibility for head movements. Choices A, B, and D are incorrect because the cervical spine does not have 2, 5, or 8 vertebrae. It is crucial to understand the anatomical structure of the spine to determine the correct number of cervical vertebrae.

Correct Answer: A

Rationale: The correct answer is A: Corpus callosum. The corpus callosum is the main commissural fiber in the brain that connects the two cerebral hemispheres, allowing for communication and coordination between them. It is the largest and most prominent commissural fiber in the brain, making it the correct choice. Summary of why other choices are incorrect: B: Anterior commissure - Connects certain regions of the cerebral hemispheres, but not as prominent or as large as the corpus callosum. C: Posterior commissure - Connects certain structures in the brainstem, not the cerebral hemispheres. D: Hippocampal commissure - Connects the two hippocampi, not the cerebral hemispheres.

Correct Answer: C

Rationale: The correct answer is C: Stenosis of aqueduct of Sylvia. This condition causes obstruction in the Sylvian aqueduct, leading to hydrocephalus with enlarged lateral and third ventricles but a normal fourth ventricle. Holoprosencephaly (A) is a midline defect, not specific to ventricle enlargement. Disorder of prosencephalon (B) is too broad and doesn't specifically address ventricle enlargement. Meningitis with blockage of arachnoid villi (D) is typically associated with communicating hydrocephalus, not specific to the aqueductal stenosis pattern seen in this case.

Correct Answer: D

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.