The number of foreign students attending Chinese universities ______ rising steadily since 1990.

A．have been

B．are

C．has been

D．is

女，34岁，闭经45天，B超示葡萄胎而行清宫术，在何种情况下不需警惕恶变

A．水泡小

B．病理示绒毛间质内血管消失

C．子宫明显大于停经月份

D．滋养层上皮细胞增生活跃

E．术前B超发现葡萄胎组织侵入肌层