Sunlight is one of the prime sources of Vitamin D for human beings. When the sun's ultraviolet rays hit the skin, a reaction takes place that enables skin cells to manufacture vitamin D.

Correct Option: D

Sunlight is one of the prime sources of Vitamin D for human beings. When the sun's ultraviolet rays hit the skin, a reaction takes place that enables skin cells to manufacture vitamin D.

Tooth enamel, along with dentin, cementum, and dental pulp is one of the four major tissues that make up the tooth in vertebrates. It is the hardest and most highly mineralized substance in the human body. It has approximately 95% calcium concentration.

Correct Option: B

Tooth enamel, along with dentin, cementum, and dental pulp is one of the four major tissues that make up the tooth in vertebrates. It is the hardest and most highly mineralized substance in the human body. It has approximately 95% calcium concentration.

With a few exceptions, all mammals and birds are warm-blooded, and all reptiles, insects, arachnids, amphibians and fish are cold-blooded. Bat is a mammal. Warm-blooded creatures, like mammals and birds, try to keep the inside of their bodies at a constant temperature. They do this by generating their own heat when they are in a cooler environment, and by cooling themselves when they are in a hotter environment.

Correct Option: C

With a few exceptions, all mammals and birds are warm-blooded, and all reptiles, insects, arachnids, amphibians and fish are cold-blooded. Bat is a mammal. Warm-blooded creatures, like mammals and birds, try to keep the inside of their bodies at a constant temperature. They do this by generating their own heat when they are in a cooler environment, and by cooling themselves when they are in a hotter environment.

Gastric glands within the stomach produce secretions called gastric juice. Hydrochloric acid (HCl) converts pepsinogen to pepsin which breaks down proteins to peptides. HCl maintains a pH in the stomach of approximately 2.0. It also dissolves food and kills microorganisms.

Correct Option: A

Gastric glands within the stomach produce secretions called gastric juice. Hydrochloric acid (HCl) converts pepsinogen to pepsin which breaks down proteins to peptides. HCl maintains a pH in the stomach of approximately 2.0. It also dissolves food and kills microorganisms.

A person with colour-blindness has trouble seeing red, green, blue, or mixtures of these colours. The most common type is red-green colour-blindness, where red and green are seen as the same colour.

Correct Option: C

A person with colour-blindness has trouble seeing red, green, blue, or mixtures of these colours. The most common type is red-green colour-blindness, where red and green are seen as the same colour.