main bottom的用法和样例：
例句
- The lithology and the weathering degree of the bed rocks are the main factors to determine their physical mechanical properties.
基岩的岩性和风化程度是决定其物理力学性质的王要因素。 - As a main method, seismic exploration can determine the depths of basement rocks and investigate the fault activity according to the extension of the fault in Quaternary layers.
作为一种主要手段，地震勘查能够查明基岩埋深，根据基岩断层向第四系地层内部的延伸可研究断层的活动性。
