Correct Answer: B

Rationale: In the given sentence, the past continuous tense 'was studying' is the most appropriate choice to indicate an ongoing action in the past. 'Was preparing' (choice A) implies a completed action rather than an ongoing one. 'Had studied' (choice C) is past perfect tense, which is not suitable for indicating an ongoing action. 'Is studying' (choice D) is present continuous tense and does not fit the past context of the sentence.

Correct Answer: B

Rationale: The correct answer is B: 'Outdated.' When something is described as 'obsolete,' it means that it is outdated or no longer in use. Therefore, an obsolete theory is no longer current or relevant. Choices A, C, and D are incorrect because an obsolete theory is not considered up to date, innovative, or necessarily scientific; it is outdated and no longer relevant in its field.

Correct Answer: B

Rationale: Medial means toward the midline of the body. In anatomical terms, 'medial' refers to positions closer to the midline of the body, which divides the body into left and right halves. Choice A is incorrect as it describes 'lateral,' which means away from the midline. Choice C is incorrect as it describes 'lateral' or 'side.' Choice D is incorrect as it describes 'inferior,' which means below or lower in position.

Correct Answer: C

Rationale: A flexible tube would be appropriate for navigating through a curved pipe as it can bend and maneuver easily within the pipe's shape. This flexibility allows the plumber to access and address any blockages or issues efficiently. Solid and rigid tubes would be challenging to use in a curved pipe due to their lack of flexibility, making navigation difficult. Perforated tubes, with holes, are not typically used for this purpose and are more suited for specific applications like drainage systems.

Correct Answer: A

Rationale: Children depend on their parents for providing basic needs like food, clothing, and shelter. 'Shelter' refers to the physical protection and housing that parents are responsible for providing to their children. While security, guidance, and affection are also important aspects of parenting, in the context of the question, the most essential need after food and clothing is shelter.