1. Bihar is India’s poorest state, with an annual per capita income of $111, lower than in the most impoverished countries of the world.
that 是指 annual per capita income 所以是单数。这道题是考比较。首先比较的两个东西必须有可比性。这道题是 the annual per capita income of Bihar 和 the annual per capita income of the most impoverished countries of the world 比较。因为,在 than 之前已经出现了annual per capita income, 所以在than 之后将它指代为that.