Explanation:

The given sentence is in the present tense and talks about a daily routine. We need to choose the correct form of the verb that matches the subject "train" and the present tense.

Subject-Verb Agreement:
In English grammar, the subject and verb in a sentence should agree in number and person. In this case, the subject is "train", which is a singular noun. Therefore, we need to use a singular verb form.

Simple Present Tense:
The simple present tense is used to describe habits, routines, and facts that are generally true. It is formed by using the base form of the verb (without any inflectional endings) for all subjects except the third-person singular (he, she, it), which requires the addition of an "s" or "es".

Options Analysis:
a)arriving - This is the present participle form of the verb "arrive", which is used in continuous tenses. It is not appropriate for describing a daily routine.
b)arrivec - This is not a valid English word.
c)arrives - This is the correct answer. It is the simple present tense form of the verb "arrive" that agrees with the singular subject "train" in the third-person singular form.
d)arrived - This is the past tense form of the verb "arrive", which indicates a completed action in the past. It is not suitable for describing a daily routine.

Conclusion:
Therefore, the correct answer is option c) "arrives". The sentence should be written as "The train arrives at 6 PM daily." This form of the verb matches the singular subject "train" and the present tense, accurately describing the daily routine.