采煤工作面基本支护方式有（）两种。

A、点柱和支架

B、密集支柱和支架

C、丛柱和金属棚

D、金属棚和锚网支护

Researchers all over the world have been seeking for determining how early infancy conceptual thinking is possible.()

A. have been seeking about determining

B. have been seeking to determine about

C. have been seeking to determine

D. have sought to determine