Nowadays many university graduates are facing the __________ about whether they should apply for a job or pursue further study to get a postgraduate diploma.[ ]

A. position

B. dilemma

C. opportunity

D. possibility

一杯水结成冰，下列说法正确的是（　　）

A．体积变小质量不变　密度不变

B．体积变小质量变小　密度变大

C．体积变大质量变大　密度变小

D．体积变大质量不变　密度变小