Explanation:

Introduction:
In this question, we are given a sentence "Its _____ third road on the left" and we need to choose the correct article from the given options.

Analysis:
To determine the correct article, we need to understand the rules related to articles:
1. "A" is used before words that begin with a consonant sound.
2. "An" is used before words that begin with a vowel sound.
3. "The" is used when we are talking about a specific noun that is already known or has been mentioned before.

Explanation of Options:
Let's analyze each given option one by one:

a) No article needed: This option suggests that no article is required in the given sentence. However, this is incorrect because every noun in English requires an article, unless it is a proper noun.

b) A: This option suggests using the indefinite article "a" before the noun. Since the word "third" starts with a consonant sound (/θ/ sound), the correct article should be "a." Therefore, this option is the correct answer.

c) An: This option suggests using the indefinite article "an" before the noun. However, the word "third" does not start with a vowel sound, so the article "an" is not appropriate here.

d) The: This option suggests using the definite article "the" before the noun. However, since we are not talking about a specific road but rather any road that is third on the left, the definite article "the" is not suitable here.

Conclusion:
Based on the analysis, the correct article for the given sentence is "a" (option b) as it is used before words that begin with a consonant sound.