Topic: Linkers or Connectors,

Best Answer Explained in Below-:

The correct answer to fill in the blank in the sentence "------ I was walking along the riverside, I saw a water snake." is "D) While." The word "while" is a conjunction that is used to indicate that two actions are happening simultaneously. In this context, it creates a temporal relationship between the speaker's action of walking along the riverside and the observation of the water snake.

Using "while" suggests that the two events occur at the same time: as the speaker is engaged in walking, they also happen to see the snake. This conveys a sense of continuity and connection between the actions, which is essential for highlighting the experience of the speaker.

In contrast, the other options do not convey the same meaning. "When" implies a specific moment rather than simultaneous actions, "because" introduces a causal relationship rather than a concurrent one, and "as because" is grammatically incorrect and does not make logical sense in this context. Therefore, "while" is the most appropriate choice, effectively illustrating the simultaneity of the two actions.