A:﹣ 54
B:﹣ 25516
C:﹣25
D:11
John shut everybody out of the kitchen ______ he could prepare his grand surprise for the party.
【提出问题】为什么有氨味?黑色物质的成分是什么?
【猜想假设】能闻到氨味说明含有铵盐(如NH4Cl);黑色固体可能有铁粉、氧化铜或二氧化锰.