请问一下：
1. IB的最高保障是$30 million 还是$150 million？ 如果是后者 他提到
30 million意义为何？
2. 里面提到maximum coverage of 或 up to an additional $30 million
中的 maximum 或up 都表示[最多赔你] 万一倒闭 客户太多 理赔金不够
有可能无法100％赔？
3. IB我记得会把客户的现金和股票交给花旗等多家银行保管
万一倒闭了 银行端都有客户资料 届时银行直接还给客户就好了
为何大费周章加买伦敦再保险？
不太懂这句话：
https://www1.interactivebrokers.com/en/index.php?f=2334&p=acc
Client securities accounts at Interactive Brokers LLC are protected by the
Securities Investor Protection Corporation ("SIPC") for a maximum coverage of
$500,000 (with a cash sublimit of $250,000) and under Interactive Brokers
LLC's excess SIPC policy with certain underwriters at Lloyd's of London 1 for
up to an additional $30 million (with a cash sublimit of $900,000) subject to
an aggregate limit of $150 million.