weed vs cigarettes Smoking pot vs. tobacco: What science says about lighting up Eating vs Smoking Cannabis: Similarities

Which of the following is an example of an attempt at minimizing threats to internal validity

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I happened upon Hegels predilection for snuff early one morning when my eyes were finally closing, and resumed, quite eagerly, this research the next evening, discovering how a tobacconist had once tried to make him the brand ambassador for a particular blend

Pipe Cleaners : Use a pipe cleaner soaked in alcohol (isopropyl or a spirit-like brandy) to clean the stem

The smokers exposures were very, very low, Kevin H Reinert, Lorillards director of regulatory science policy, testified in a deposition in April I dont believe it increased the risk. Plaintiffs have found this hard to challenge, since Lorillard failed to preserve most of the original test reports