According to the passage, the more protein a rat consumes, the lower will be the
A. ratio of the rat" s blood-tryptophan concentration to the amount of serotonin produced and released in the rat"s brain.
B. ratio of the rat"s blood-tryptophan concentration to the concentration in its blood of the other amino acids contained in the protein.
C. ratio of the rat"s blood-tyrosine concentration to its blood-leucine concentration.
D. number of neurotransmitters of any kind that the rat will produce and release.
E. number of amino acids the rat" s blood will contain.
高层住宅设计中，候梯厅深度不应小于多台电梯中最大轿箱的深度，且不得小于()m。
A. 1.2
B. 1.5
C. 1.8
D. 2.1
According to the passage, when the authors began their first studies, they were aware that
A. they would eventually need to design experiments that involved feeding rats high concentrations of protein.
B. tryptophan levels in the blood were difficult to monitor with accuracy.
C. serotonin levels increased after rats were fed meals rich in tryptophan.
D. there were many neurotransmitters whose production was dependent on metabolic processes elsewhere in the body.
E. serotonin levels increased after rats were injected with a large amount of tryptophan.
提升装置使用中的钢丝绳做定期检验时，安全系数为下列情况之一的，必须更换:专为升降人员用的小于（）
A. 5
B. 6
C. 7
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