Answer:
C. The ash mixed with the typhoon's rain became too heavy for roofs to support.
Step-by-step explanation:
In the article, the eruption caused an ash cloud to be formed which mixed with the droplets from the rain. When the watery ash fell on roofs, its weight was to heavy to be supported by the roofs, thus the roofs started collapsing. Thousands of roofs collapsed due to this effect.
Therefore, the appropriate answer is: the ash mixed with the typhoon's rain became heavy for roofs to support.