She worked really hard on the project.

The suffix -ed in the italicized word in the sentence above illustrates that the work happened in the past tense.

Correct.

To understand how the suffix -ed in "worked" indicates past tense, we can look at the rules of English verb conjugation.

In English, verbs have different forms depending on the tense. The -ed suffix is added to regular verbs to indicate the past tense. For example, the base form of the verb "work" remains unchanged, but when we want to express that the action took place in the past, we add -ed to form "worked."

Here's a step-by-step breakdown of how to determine if a verb is in the past tense using the -ed suffix:

1. Identify the base form of the verb: In this case, the base form is "work."
2. Check if the verb is irregular: Some verbs have irregular forms in the past tense that don't follow the -ed rule (e.g., "go" becomes "went"). However, "work" is a regular verb, so we can use the -ed suffix.
3. Add -ed to the base form: Now, we add -ed to "work," resulting in "worked."
4. Determine that the verb is in the past tense: The addition of -ed indicates that the action of "work" happened in the past.

So, in the sentence provided, the suffix -ed in "worked" indicates that the action of working on the project happened in the past tense.