1926年，萨姆纳（Sumner）首先制得（）结晶，并指出酶的本质是（）。他因这一杰出贡献，获1947年度诺贝尔化学奖。
参考答案：脲酶；蛋白质
After studying in a medical college for five years, Jane _____ her job as a doctor in the countryside. [ ]
A. set out
B. took over
C. took up
D. set up
滴点是表示润滑脂的耐热性能好坏的质量指标。
