Answer:
Option D, has only a single opening
Explanation:
A gastrovascular cavity has only one opening. The food goes in and comes out of the same opening there by making it a two way digestive tract.
However, a digestive tube is a one way digestive tract where the food goes in from mouth (one end) and comes out of anus (second end) . It is also called as alimentary canal
Hence, option D is correct
Answer:
Option C. The number of oxygen atoms is the same before and after the reaction.
Explanation:
When hydrogen combine with oxygen, water is formed. According to law of conservation of matter, matter cannot be created nor destroyed during a chemical reaction. So according to this law, the amount of reactants is equal to the amount of product produced after a chemical reaction and the number of oxygen atoms is the same before and after the reaction.
An ecosystem is a community of biological organisms that interact within their overall environment. One level up from this is a biome which is a very large geographical area which consists of very particular biological communities that share a similar environment and ecosystem.
