A pilot study is

Correct Answer: B

Rationale: A pilot study tests feasibility before a full research project. 'A small scale study conducted in advance...,' is correct, describing its role in refining methods and logistics, per research methodology (e.g., Polit & Beck). 'A scientific study carried out on pilots,' misinterprets pilot.' 'The first and most important step,' overstates its priority; it's optional. 'A study conducted simultaneously...,' is incorrect; pilots precede, not parallel, main studies. B's focus on pre-testing feasibility matches standard practice, making it the accurate answer.

Correct Answer: C

Rationale: Cardiac output (CO) is heart rate (HR) times stroke volume (SV). Given HR = 84 bpm and SV = 60 ml (0.06 L), CO = 84 × 0.06 = 5.04 L/min, approximated as 5 L/min. '5 L/min,' is correct, per physiology (e.g., Guyton). The question's exercise scenario (13 L/min) is post-exercise, but initial CO aligns with resting values. Choices A, B, and D miscalculate. C's accuracy makes it the answer.

Correct Answer: D

Rationale: Antigen-presenting cells (APCs) process and display antigens to T-cells, initiating adaptive immunity. 'Natural killer cells,' is correct as the exception, per immunology references like Abbas' Basic Immunology, as NK cells target infected cells directly, not presenting antigens. 'Macrophages,' engulf pathogens and present antigens via MHC. 'Dendritic cells,' are potent APCs, activating naive T-cells. 'B-Lymphocytes,' present antigens to helper T-cells for antibody production. NK cells' innate cytotoxic role, lacking MHC presentation, distinguishes D as the accurate answer, separate from APC functions.

Correct Answer: B

Rationale: The uterine (fallopian) tube is about 10 cm long, extending from ovary to uterus. '10 cm,' is correct, per anatomy texts like Netter's Atlas, varying slightly (7-12 cm) but typically cited as 10 cm. '5 cm,' is too short. '15 cm,' and '20 cm,' exceed average length. The tube's role in ovum transport supports B's accuracy, reflecting standard anatomical measurements.

Correct Answer: C

Rationale: Essential amino acids must be dietary, as the body cannot synthesize them. 'Alanine,' is correct as the exception, a non-essential amino acid produced from pyruvate, per biochemistry (e.g., Nelson). 'Leucine,' 'Lysine,' and 'Valine,' are essential, required from food. Alanine's endogenous synthesis contrasts with the dietary need for others, making C the precise answer.