A:铕属于非金属元素
B:铕的原子序数是63
C:铕原子中质子数为63
D:铕的相对原子质量为152.0
甲地海拔为8848米,乙地海拔为﹣400米,则甲,乙两地的相对高度为( )
He has ________ in touch with his foreign friends for many years.