Answer:
before.
Step-by-step explanation:
In English language, a conjunction can be defined as an English word that is typically used for connecting two or more clauses, words, phrases or sentences. Some examples of conjunction are but, and, although, because, or, yet, after, before, if, how, once, since, until, unless, when, so that, etc.
A subordinate conjunction can be defined as an English word that joins or connects an independent clause and a dependent (subordinate) clause. Thus, this type of conjunctions are used at the beginning of a dependent (subordinate) clause.
An independent clause can be defined as a clause that expresses a complete thought while standing alone as a simple sentence and comprises of at least a subject and a verb (predicate).
A dependent clause can be defined as a type of clause that is inserted into another clause to make meaning or express a complete thought.
In this scenario, the dependent (subordinate) clause is "the programme began" and as such would require a subordinate conjunction at the beginning; to join it with the independent clause "The Principal permitted us."
Hence, the complete sentence would be written as follows;
"The Principal permitted us before the programme began."