The asphalt at La Brea seeps to the surface, especially in the summer, and forms shallow puddles that would often have been concealed by leaves and dust.
句意：拉布雷亚的沥青会渗漏到地表，尤其是在夏天，会形成浅水坑，这些水坑通常会被树叶和灰尘所掩盖。conceal掩盖。highlight强调。cover覆盖。与conceal意思最接近。transform转换。contaminate污染。因此，本题的正确答案为B。