From early times, the Adige Valley, which delimits Valpolicella to the west, was a major communications route connecting southern, eastern and northern Europe.
In this sentence, delimits means:

• Delimit (verb):

English Meaning: to fix or define the limits of.
Bangla Meraning: সীমা বা সীমানা নির্দেশ করা।

Synonyms: bound, circumscribe, define, demarcate, demark, limit.

Other options:
(খ) Oppose- acts in opposition to; fights against or resists strongly; বিরোধিতা করা।
(গ) Anterior- Describes the front or direction toward something; পূর্ববর্তী; পূর্বগামী।
(ঘ) Enhance- increases or further improves the quality or value of; বাড়ানো; বৃদ্ধি করা।

Source: Accessible Dictionary by Bangla Academy and Oxford Learner's Dictionary.