(A) Small Intestine

The absorption of nutrients from food primarily occurs in the small intestine. The small intestine is a long, coiled tube that follows the stomach in the digestive tract. It is the primary site for the absorption of nutrients such as sugars, amino acids, fatty acids, vitamins, and minerals into the bloodstream. The small intestine has specialized structures called villi and microvilli that increase its surface area, facilitating efficient absorption of nutrients. The large intestine primarily absorbs water and electrolytes but is not the main site for nutrient absorption. The stomach plays a role in digestion but is not a major site of nutrient absorption. The liver is involved in processing and storing nutrients but does not directly absorb them from the digestive tract.

Answer: B) They are the sites at which microtubules attach to chromosomes. Explanation: They are the sites at which microtubules attach to chromosomes.

Answer: A) transcription Explanation: Protein synthesis at the ribosome is immediately preceeded by the transcription process.

Answer: C) Mitochondria Explanation: Cellular respiration is the multi-step process that creates energy from nutrients and food molecules. It begins in the cytoplasm of the cell, with the mitochondria functioning as the main organelle where the rest of the process continues and finishes. During respiration, glycolysis occurs in the cytoplasm of the cell.

The substance that causes the clotting of blood is:

(A) Thrombin

Thrombin is an enzyme that plays a crucial role in the blood clotting process. It is responsible for converting fibrinogen, a soluble plasma protein, into insoluble fibrin threads. These fibrin threads form a mesh that helps in the clotting of blood, particularly at the site of injury or wound. Therefore, option (A) Thrombin is the correct answer.