Choose the correct statement-

Options

A. Many species of Porphyra, Laminaria and Sargassum are among 70 species of marine algae used as food.
B. Agar is used to grow microbes and in preparations of ice-creams and jellies.
C. Algae are useful to man in a variety of way
D. All

Answer

To solve the question "Choose the correct statement," we will evaluate each option provided regarding marine algae and their uses.

### Step-by-Step Solution:

1. **Understand the Question**: We need to identify which statement about marine algae is correct. The options involve various facts about algae, their species, and their uses.

2. **Evaluate the First Statement**:
- The first option states that "Many species of Porphyra, Laminaria, and Sargassum are among 70 species of marine algae used as food."
- **Analysis**: Porphyra, Laminaria, and Sargassum are indeed known species of marine algae that are consumed as food. This statement is correct.

3. **Evaluate the Second Statement**:
- The second option mentions that "Agar is used to grow microbes and in the preparation of ice cream."
- **Analysis**: Agar is a gelatinous substance derived from red algae, specifically from species like Gelidium and Gracilaria. It is widely used in microbiological media and as a thickening agent in food, including ice cream. This statement is also correct.

4. **Evaluate the Third Statement**:
- The third option suggests that "Some algae are a rich source of proteins and are used as a food supplement."
- **Analysis**: Many algae, particularly spirulina and chlorella, are indeed rich in proteins and are used as dietary supplements. This statement is correct.

5. **Conclude**:
- Since all the statements provided in the options are correct, the final conclusion is that the correct option would be "All" (the fourth option).

### Final Answer:
The correct option is **4th: All statements are correct.**

---