Nacre, also known as the mother of pearl, is an organic-inorganic composite material produced by some molluscs as an inner shell layer; it also makes up the outer coating of pearls. It is strong, resilient, and iridescent. So, the correct option is A. ( A hard iridescent substance forming the inner layer of certain shells )

Snakes lay eggs and are hence Oviparous and not Oviparous.

Mammals are the warm-blooded vertebrate animal that is distinguished by the possession of hair or fur, females that secrete milk for the nourishment of the young. They give birth to young ones so they are known as viviparous.
So, the correct answer is 'Mammals'.

Pollen grains form the first cell of male gametophytic generation.It divides into two unequal cells; a small generative cell and a larger vegetative cell. During the germination of pollen tube over the carpel, the vegetative tube nucleus migrates into the pollen tube and reaches up to the distal end. The generative cell also migrates into the pollen tube and divides to form two male gametes. Each male gamete consists of a large nucleus surrounded by a thin sheath of cytoplasm. 

Homosporous pteridophytes produce only one type of spores. Also, all the sporangia in a homosporous pteridophyte are similar.

• In angiosperms, as the pollen tube penetrates the ovule, it releases two sperm cells. One fuses with the egg to create a diploid zygote which develops into an embryo, while the other joins with the fusion nucleus to form a triploid nucleus that develops into endosperm.
  
• So the correct answer is ' Diploid'.

Anal style are a pair of thread like appendages arising from the 9th segment of the male cockroaches. They are characteristic feature of male cockroaches and help in copulation.

Cockroach blood is not red because they do not use hemoglobin to carry oxygen. In fact, their bloodstream is not used to carry oxygen either. They use a system of pipes called tracheae to bring the oxygen and remove carbon dioxide from their tissues and oxygen goes directly into tissues by diffusion. So, the correct option is A. ( Oxygen goes directly into tissues by diffusion )

An adult human being has approximately 100 000 billion cells, all originating from a single cell, the fertilized egg cell.

• Bryophytes are known as the amphibians of plant kingdom because they need water for fertilisation. The sperms of bryophytes are flagellated and reach the eggs by means of swimming in water. On the other hand, pteridophytes do not need water for fertilisation.
• Bryophytes have gametophyte as dominant phase of life on which sporophyte is dependent whereas Pteridophytes have sporophyte as dominant phase but sporophyte is not dependent on gametophyte.
• Heterospory is the formation of two types of spores which are different in size i.e. large spores and small spores. Large spores are called megaspores while small spores are called microspores. Spores are formed by the sporophyte both in bryophytes and pteridophytes.