Acetylene is the only fuel gas suitable for gas welding because of its favourable flame characteristics of both high temperature and high propagation rates. Other fuel gases, such as propane, propylene or natural gas, produce insufficient heat input for welding but are used for cutting, torch brazing and soldering.

(B) Urethra

The urethra is the structure that forms a common passage for both urine and sperm in human males. It connects the urinary bladder to the external opening and serves as the channel through which urine and semen pass out of the body. The other options—Oviduct, Ureter, and Vas deferens—are not involved in the passage of urine in males. Oviduct is part of the female reproductive system, while the ureter carries urine from the kidneys to the bladder, and the vas deferens is a duct that transports sperm from the testes to the urethra.

(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.