Two Separate Studies Examine the Potential Association Between Occupation Type

Multiple Choice

Two separate studies examine the potential association between occupation type and voter participation.The first advertises online for participants and asks those who respond to tell the researchers in-depth accounts regarding their paid work and their voting behaviors for the last three years.The second study randomly selects 200 respondents and asks them to complete a standardized set of survey questions about their paid work and voting behaviors over the past five years.The first study observes a patterned relationship between work and voting,while the second study does not.The reason the second study's results are more valid is that the

A) first study is based on experimental data,which are less reliable.
B) second study is based on a probability sample.
C) second study is based on more years of data on voting behaviors.
D) first study does not allow us to infer causality,but the second does.