Answer:
A). Mr. Duarte was packing some boxes.
B). Mrs. Duarte was locking the car door.
C). Jeff was holding the armchair.
D). Speedy was pushing a ball in his mouth.
E). A box was falling to the floor.
Explanation:
Past Continuous tense is primarily employed to denote an 'on-going action of the past' that started in a time before now and continued for a while(in the past). It is formed by using the auxiliary verb 'was/were'(to denote past) followed by the progressive form of the main verb('verb + ing' to reflect the continuity). The given sentences could be filled by using this rule to signal to the progression of the action in the past.