The correct answer is option 'c) Simple past tense'.

A diary entry is a personal account of events and experiences that have already happened. Therefore, it is most appropriate to write a diary entry in the simple past tense. This tense is used to describe actions or events that occurred in the past and have already been completed.

The simple past tense is formed by adding "-ed" to regular verbs, while irregular verbs have specific past tense forms. Here are a few examples of how the simple past tense is used in diary entries:

1. "Today, I woke up early and went for a jog."
2. "I met my friend at the park, and we played basketball together."
3. "In the afternoon, I finished reading an interesting book."
4. "After dinner, I watched a movie with my family."

By using the simple past tense, the writer is able to effectively convey the sequence of events and provide a clear and concise account of their day. This tense creates a sense of immediacy and helps the reader to feel as if they are experiencing the events alongside the writer.

It is important to note that other tenses, such as the present continuous tense, present perfect tense, or future tense, are not appropriate for writing a diary entry. The present continuous tense is used to describe actions that are happening at the moment of speaking, while the present perfect tense is used to describe past actions that have a connection to the present. The future tense is used to describe actions that are yet to happen.

In conclusion, a diary entry should be written in the simple past tense as it accurately reflects the nature of a personal account of past events. This tense allows the writer to provide a chronological and detailed description of their experiences in a diary entry.