短语讲解：

1. The Defense Department confirmed at least 1,584 cases of sexual abuse against military dependents over four years ending in 2014.

at least 至少
例句：In fact it requires at least n generators.
事实上，它至少要有n个元素。

2. A lack of transparency in military courts blocks a clear picture of child sex abuse, says the AP.

a lack of 缺乏，缺少
例句：Hard work can often make up for a lack of intelligence.
勤奋工作往往可以弥补智力的不足。