本视频对应复杂句子分析实践案例：
- Although a surge in retail sales has raised hopes that a recovery is finally under way, many economists say that without a large amount of spending the recovery might not last.
- Although various eighteenth- and nineteenth-century American poets had professed an interest in Native American poetry and had pretended to imitate Native American forms in their own works, it was not until almost 1900 that scholars and critics seriously began studying traditional Native American poetry in native languages.
- Of all the vast tides of migration that have swept through history, perhaps none was more concentrated than the wave that brought 12 million immigrants onto American shores in little more than three decades.
