—Never mind. I _______________ here for only a few minutes.
A:came
B:have been
C:have come
N是重要的非金属元素,尿素、羟胺、硝酸、亚硝酸钠均为重要的含氮化合物.
“含羞草的叶受到碰触会合拢”所表现出的生物特征是( )