1(One of the problems)A of United States agriculture that has persisted (during the)B 192 0's until the present day is the tendency of farm income to lag (behind)C the coasts of (production)D.

1.B.错, 应为from the 1920's until the present day 从二十世纪20 年代直到现在。

2.from 时点A until 时点B, 为固定搭配, 表示从时点A 直到 时点B.
例句:
(1) Philanthropic foundations and the promoting of science
and scientific culture in Europe from the 1920's until the present day.
(2) The optimization of simulations is a challenging optimization problem that researchers have attacked for many years from the 1950's
until the present day.

3.还有,使用until需注意的问题——until引导的时间状语(从句)前不可有表示“段时间”和“段距离”的状语。例如：

1)我等了两天，一直等到见到他。

　　不可说：I waited for two days until I met him.

　　可说：I had waited for two days before I met him.

2)我们向东走了一百公里，直到见到水和草。

　　不可说：We walked eastward for 100 kilometers until we saw water and grass.

　　可说：We had walked eastward for 100 kilometers before we saw water and grass.

4.英文中没有楼上提及的........since ......until 的惯用组合.