Given a passage with a context and an answer, construct a question on the basis of the information present in the passage. Construct the question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) it answer uses text phrases from the passage. Avoid creating questions that (i) can't be answered correctly without actually understanding the passage and (ii) uses the same words or phrases given in the passage.

Example Input: Context: In atherogenesis, dendritic cells, beside presenting antigens, may be sources of tumour necrosis factor (TNF)alpha and nitric oxide (NO), together with mast cells and smooth muscle cells.', 'We have looked at the expression of TNFalpha and inducible NO synthase (iNOs) by these cells by affinity cytochemistry in autoptical specimens from normal carotid arteries and not ruptured, hemorrhagic or calcified atheromata.', 'Round to dendritic, major histocompatibility complex class II molecules (MHC-II+) cells and avidin-labeled mast cells were rare in normal arteries and significantly more numerous in atheromata. Many MHC-II+ cells expressed S-100 antigen; while a few were positive for phalloidin; appreciable fractions of these cells were immunoreactive for TNFalpha and iNOs, both in control specimens and atheromata. The fraction of mast cells labeled for iNOs was significantly lower in atheromata than in controls. Phalloidin positive cells were the most abundant cell type in the normal intima and atheromata; the fractions of these cells labeled for TNFalpha and iNOs were significantly higher in atheromata than in controls. Very few of these cells were also labeled for MHC-II. Computerized image analysis confirmed that the amounts of iNOs and TNFalpha were higher in atheromata than in controls. The increase in TNFalpha in atheromata was also confirmed by western blot.
Answer: Dendritic cells and mast cells can participate to the generation of TNFalpha and NO in the normal arterial wall and in atheromata, but myointimal cells are candidates as major sources of these molecules.
Example Output: Are smooth muscle cells , dendritic cells and mast cells sources of TNFalpha and nitric oxide in human carotid artery atherosclerosis?

Example Input: Context: Spinal anesthesia can be challenging in patients undergoing total joint arthroplasty because of poorly palpable surface landmarks and age-related changes in the lumbar spine. We hypothesized that pre-procedural ultrasound imaging would be effective in identifying the lumbar intervertebral spaces and would provide an accurate measure of the depth to the intrathecal space.', "Fifty patients undergoing elective total joint arthroplasty were recruited in this prospective descriptive study. Using a curved-array 2-5 MHz transducer, the lumbar spine was imaged in two views, i.e., longitudinal parasagittal (LP) and transverse midline (TM). The intervertebral levels were identified by counting upwards from the sacrum. The locations of the interlaminar spaces were identified by visualizing the ligamentum flavum-dura mater complex and the posterior aspect of the vertebral body. The needle insertion point for a midline approach was determined from the ultrasound examination and was marked on the skin of the patient's back.", 'The mean patient age was 67 +/- 10 yr, and 46% of the patients had a body mass index >30 kg . m(-2). Surface landmarks were difficult or impossible to palpate in 38% of the patients. The scan quality on the LP and TM views was adequate or better in 100 and 98% of the patients, respectively. Dural puncture was achieved with one needle insertion attempt and within two needle insertion attempts in 84% and 98% of the patients, respectively. The ultrasound-measured depth to the intrathecal space correlated well with the actual needle insertion depth (concordance correlation coefficient = 0.82, accuracy 0.95, precision 0.86), with a tendency to overestimate the depth by just 2.1 +/- 5.4 mm.
Answer: Ultrasound imaging of the lumbar spine provides clinically useful information that can facilitate spinal anesthesia in the older orthopedic patient population.
Example Output: Does an ultrasound-assisted approach facilitate spinal anesthesia for total joint arthroplasty?

Example Input: Context: We tested for the presence of erythropoietin receptor (Epo-R) in human skeletal muscle and alterations in gene expression after prolonged use of an erythropoiesis-stimulating agent (ESA).', 'Nine healthy men were treated with ESA for 10 weeks (darbepoietin alfa). Muscle biopsies were collected before and after treatment. Alterations in gene expression were evaluated by gene array. Western blot and PCR analysis were used to test for Epo-R presence in human skeletal muscle.', 'Very low Epo-R mRNA levels were found, but a new and sensitive antibody did not identify Epo-R protein in human skeletal muscle. The between-subject variation in skeletal muscle gene expression was greater than that observed in response to prolonged ESA treatment.
Answer: Erythropoietin is unlikely to exert direct effects in human skeletal muscle due to a lack of Epo-R protein. Furthermore, prolonged ESA treatment does not seem to exert either direct or indirect effects on skeletal muscle gene expression.
Example Output:
Does prolonged erythropoietin treatment impact gene expression in human skeletal muscle?