The given sentence talks about completing the order in the past, as can be inferred from the word 'arrived' which is in simple past form.
Past tense expresses an action or situation that was started and finished in the past. Most past tense verbs end in “-ed”. The irregular verbs have special past tense forms which must be memorized, like "left" is the past form of leave. For example – Last night, I finished my entire holidays homework.
Option A is in past continuous form and cannot be used here as it expresses an action that started and continued irrespective of another action in the past.
Option C is in past perfect form which is incorrect here as it is used to express actions that started and got completed before another action in the past.
Option D is incorrect here as 'would' is used to express sentences in subjunctive mood.
Option B is in simple past form and is the right choice here, as it indicates that an action (order) got completed in the past. Therefore Option B is the correct answer.