Answer:
D. There is no enough oxygen in the culture fluid
Explanation:
The cells in the test tube need to carryout one of the important metabolic processes of living organisms - respiration. The process involves the breakdown of glucose to generate energy for other metabolic processes in the cell.
Respiration can be carried out in the presence of oxygen (aerobic) or in the absence of oxygen (anaerobic). Human cells are primarily aerobic but can carryout respiration anaerobically in the presence of inadequate oxygen.
For aerobic respiration, glucose is broken down in the presence of oxygen to produce carbon-dioxide, water and energy in the form of ATP:

<em>In the absence of oxygen, the glucose becomes converted to lactic acid and a smaller amount of ATP is produced as compared to aerobic respiration.</em>
<em>Hence, lactic acid gradually builds up in the absence of oxygen due to anaerobic respiration.</em>
The correct option is D.
Answer;
-Keratinized stratified squamous epithelium forms the epidermis of the skin.
-In keratinized stratified squamous epithelial tissue, the cells on the apical (outer) surface are dead.
Explanation;
-Stratified squamous epithelium is a type of tissue found covering and lining parts of the body. Stratified squamous epithelium may be keratinized or nonkeratinized. Non-keratinized surfaces must be kept moist by bodily secretions to prevent them from drying out.
-The cells on the surface of stratified squamous keratinized epithelium are very flat. Not only are they flat, but they are no longer alive. They have no nucleus or organelles. They are filled with a protein called keratin, which is what makes our skin waterproof.
B. group of the same species that live together.