Final answer:
The correct answer is option 'd', as 'Underneath' is not an adverbial conjunction but a preposition, which is used to indicate location or positioning rather than connecting clauses.
Step-by-step explanation:
The question asks to identify which of the given options is not an adverbial conjunction. An adverbial conjunction is a word that connects two clauses together and modifies or describes verbs, adjectives, or other adverbs. Notably, it helps to signal the relationship between the two clauses, such as contrast, cause, or effect.
From the list provided a. However, b. Thus, c. Consequently, these are all adverbial conjunctions as they can connect two independent clauses indicating a transition. The word 'However' shows contrast, 'Thus' and 'Consequently' show a result or effect. On the other hand, d. Underneath is not an adverbial conjunction but a preposition that indicates the physical relationship of one thing to another, commonly used to describe the location of something.
Therefore, the correct answer is option 'd'. Underneath is not an adverbial conjunction.