Introduction:
The correct option to fill in the blank is option 'D' - is trying. This answer is correct because it matches the present continuous tense and conveys the ongoing action of Noriko studying for her ESL test.

Explanation:
In the given sentence, the phrase "to study for her ESL test" indicates that Noriko is currently engaged in the activity of studying. To express this ongoing action, we need to use the present continuous tense.

The present continuous tense is formed using the auxiliary verb "to be" in the present tense (is/are/am) followed by the present participle form of the main verb (trying).

Example:
Let's consider the sentence, "Noriko is trying to study for her ESL test."

Subject-Verb Agreement:
In the sentence, "Noriko" is the subject, and as a singular noun, it requires the singular form of the verb. Therefore, the correct form of the verb is "is trying."

Present Continuous Tense:
The present continuous tense is used to describe an ongoing action happening at the present moment. In this case, Noriko is currently studying for her ESL test.

Other Options:
- Option 'A' - try: This option does not match the present continuous tense and does not convey the ongoing action. It would suggest that Noriko attempts to study for her ESL test, but it does not indicate that she is currently doing so.
- Option 'B' - tries: This option is in the simple present tense, which does not match the context of the sentence. It would imply that Noriko habitually studies for her ESL test, but it does not indicate the current action.
- Option 'C' - tried: This option is in the simple past tense, which does not match the ongoing action in the present. It would suggest that Noriko studied for her ESL test at a specific time in the past.

Therefore, the correct answer is option 'D' - is trying, as it accurately reflects the present continuous tense and the ongoing action of Noriko studying for her ESL test.