单项选择。
Mary and her father ______ in Beijing last month. [ ]
A. was
B. were
C. are
D. is
答案:B
空气的体积质量是1.239×10-3g/cm3 ,用小数把它表示出来为( )g/cm3
提高挫折承受力的关键在于()
A、平时训练
B、稳定情绪
C、丰富的经历
D、坚强的意志