Although bullfrogs were introduced into mainland China in 1959, they were not wildly raised until 1990.是什么意思？

Although bullfrogs were introduced into mainland China in 1959, they were not wildly raised until 1990.

1959年牛蛙被引入中国大陆, 但直到1990年才开始在国内大范围饲养.

although

conj. 尽管，虽然，但是，然

例句
He was in love with her, although he did not put that name to it.
他爱着她，虽然他没有将其称为爱。

bullfrogs

n. 牛蛙，菜蛙( bullfrog的名词复数 )；

例句
Although bullfrogs were introduced into mainland China in 1959, they were not wildly raised until 1990.
1959年牛蛙被引入中国大陆, 但直到1990年才开始在国内大范围饲养.

were

be的过去时复数和第二人称单数形式，有时代替 was,用于条件从句、动词 wish 之后等；

例句
Shops, houses, and vehicles were set ablaze.
店铺、房子和车辆全都陷于火海。

introduced

adj. [医]引种的，引进的；v. 提出( introduce的过去式和过去分词 )，介绍，引进，作为…的开头；

例句
The changes will be introduced in April...
这些变更将于4月开始实行。

into

prep. （表示方向）进入…中，（表示所属）输入，（表示状态）进入…状态，（表示时间）持续到；

例句
By 1838, the abolitionists had shamed parliament into ending slavery in British colonies...
到1838年，废奴主义者迫使议会出于道德压力而废除了英国殖民地的奴隶制。

mainland

n. 大陆，本土；adj. 大陆的，本土的；

例句
The car ferries from the mainland are often fully booked by February.
从大陆出发的汽车轮渡常常在2月前就被预订一空。

china

n. 中国；

例句
In China Grace Thompson observed the great variety of loads that were carried by 'slim, erect but muscular Amazons'.
在中国，格雷丝·汤普森看见“苗条、挺直而强健的女人们”携带着各种物品。

in

prep. 采用（某种方式），穿着，带着，（表示位置）在…里面，（表示领域，范围）在…以内，（表示品质、能力等）在…之中；adv. 在家，进入，到达，流行，当选；adj. 在内的，朝内的，在位的，执政的，[口语]流行的，时髦的，（车等）到站的；n. 执政党，掌权者，知情者，<美口>入口，门路，<体>（板球或棒球）攻球的一方；

例句
There was a terrible sadness in her eyes...
她眼神中流露出深深的悲伤。

they

pron. 他/她/它们，人们，大家，政府，当局，她们；

例句
The storms had abated by the time they rounded Cape Horn.
他们绕过合恩角时，暴风雨已经减弱。

not

adv. 不，[用以表示否定、否认、拒绝、禁止等]不是，几乎不，未必，没有[用于否定后面的词或短语]；

例句
It became very clear that the incident was not just an aberration, it was not just a single incident.
事实已经很清楚，这件事不是偶发的，它并不是一起孤立的事件。

wildly

adv. 疯狂地，粗暴地，野蛮地，野生地，失去控制地；

例句
He stumbled, clawed wildly at the air and fell backwards into the water.
他绊了一脚，双手在空中胡乱抓了几下，然后仰天栽进了水里。

raised

adj. 凸起的，浮雕的，有凸起花纹的，发酵的；v. 引起( raise的过去式和过去分词 )，提高（价格等），提起，唤起；

例句
His family raised the alarm when he had not come home by 9pm.
等到晚上9点他还未回家，他的家人便报警了。

until

prep. 到…为止，在…以前；conj. 到…为止，在…以前，直到…才；

例句
The threat is likely to remain in abeyance until next year's meeting in Reykjavik.
这一威胁很可能会一直存在下去，直至明年的雷克雅未克会议。