It occurs chiefly as stannic oxide , SnO 2 in cassiterite.主要以氧化物状态存在.One of the key problems in its origin is the solubility of cassiterite in granitic melt.锡石在花岗质熔体中的溶解度,是阐明花岗岩全岩型锡矿成因的关键....
他们考虑来自外部的感染公司的病毒, 他们设想黑客侵入到信息宝库中.They think of viruses that infect an organization from the outside. They envision hackers breaking into their information vaults.现在来自外部的结婚压力少了。Nowadays there are fewer extrinsic pressures...