Teacher:In this task, you're given a statement, and three sentences as choices. Your job is to determine which sentence clearly disagrees with the statement. Indicate your answer as '1', '2', or '3' corresponding to the choice number of the selected sentence.
Teacher: Now, understand the problem? Solve this instance: Statement: Beyond their impacts as separate emissions, SO2, NOx, and mercury together contribute to many air pollution-related problems affecting human health and the environment. Choices: 1. Mercury is the most dangerous of the three elements. 2. Separately, the elements are harmless, but together create a toxic substance. 3. Air pollution has many adverse health effects in humans.
Student:
2