ABS树脂是下列哪几种物质的共聚物:()。
A.丙烯晴、乙烯
B.丙烯晴、1,3一丁二烯、苯乙烯
C.丙烯晴、1,3一丁二烯
D.乙烯晴、苯
参考答案:B
解析:
She and her family hid away for nearly twenty-five months _____ they were discovered.
A.After
B.since
C.until
D.before
危机的类型不包括()
A.发展性危机
B.境遇性危机
C.存在性危机
D.疾病危机
E.以上都是