Read the Following USGS Statement and Answer This Question

Multiple Choice

Read the following USGS statement and answer this question.
USGS Statement on Bluebird Canyon Landslide in Laguna Beach, California
In the early morning of June 1, 2005, a landslide began moving in the Bluebird Canyon area of Laguna Beach, California. No rainfall or earthquake activity occurred during or immediately before the landslide movement. This movement is almost certainly related to the extremely heavy winter rains that occurred from December through February. Rainfall from the winter season has been slowly percolating downward through the soil and is gradually raising ground-water levels. As ground water rises, slopes can become unstable and begin to move, even if no rain is presently occurring. The current landslide might enlarge to include areas upslope or other adjacent areas within the next few days and weeks.
The continuing infiltration of water from the winter rainy season could trigger other deep landslides in the southern California region over the next few weeks and months. (from www.usgs.gov/homepage/ landslide_laguna.asp)
-What empirical data are mentioned here as a cause for the mass wasting?

A) Rainfall
B) Rising groundwater levels
C) Earthquake levels