The theory of natural selection was proposed jointly by Charles Darwin and: MCQ with Answer and Explanation

Explanation:
Cholera is a severe diarrheal disease caused by the bacterium Vibrio cholerae. AIDS is caused by the Human Immunodeficiency Virus (HIV), which is a retrovirus. Dengue fever is transmitted by the bite of an infected female Aedes aegypti mosquito, not Culex (which transmits filariasis and Japanese encephalitis). Thus, statements 1 and 2 are correct.

Explanation:
The spleen is the largest lymphoid organ in the body. It is located in the abdominal cavity, specifically in the upper left quadrant, tucked between the stomach and the diaphragm, protected by the rib cage (ribs 9-11). It functions primarily in filtering blood, removing old or damaged red blood cells, storing platelets, and mounting immune responses against blood-borne pathogens. It is not located in the thoracic, pelvic, or cranial cavities.

Explanation:
The Calvin cycle fixes CO₂ into glucose, which is the primary organic product of photosynthesis. Oxygen is a byproduct of water splitting.