The correct answer is option 4, which states that all the options are correct.

To better understand the options:

Option 1 states that only Euglena and Amoeba are examples of unicellular organisms.

Option 2 states that only Euglena and Paramecium are examples of unicellular organisms.

Option 3 states that only Amoeba and Paramecium are examples of unicellular organisms.

However, the correct answer is option 4, which states that all the options are correct. This means that all three organisms mentioned - Euglena, Amoeba, and Paramecium - are examples of unicellular organisms.

Unicellular organisms are those that consist of a single cell and carry out all the necessary functions for life within that single cell. These organisms are capable of performing all life processes, such as reproduction, metabolism, and responding to the environment, within a single cell.

Therefore, the correct answer is option 4, as all the mentioned organisms - Euglena, Amoeba, and Paramecium - are examples of unicellular organisms.