Plants Are Sometimes Used for Phytoremediation in Areas Where the Soil

Plants are sometimes used for phytoremediation in areas where the soil has been contaminated with heavy metals. Suppose the Acme Remediation Company is proposing to remediate a contaminated area that you wish to restore. Acme presents you with the following data as evidence of their company's ability to remediate soil.

-What likely caused the loss of metals in the control soil?

A) being washed away by water draining through the soil
B) evaporation of the metal molecules into the air
C) absorption of the metal molecules by clay particles
D) buildup of humus