Why were soldiers on both sides most afraid of poisonous gas?

Amarketing research firm wants to determine the most effective method of selling furniture: print, radio, television, or online. they recruit 310 volunteers to participate in the study. the researcher segments the volunteers by level of income. of the 310 volunteers, 80 earn below $ 20 comma 000, 60 earn between $ 20 comma 000 and $ 40 comma 000, 110 earn between $ 40 comma 000 and $ 60 comma 000, and 60 earn over $ 60 comma 000. the volunteers from each group are randomly assigned to either the print advertising group, the radio group, the television group, or the online group. each group is exposed to the advertising. after 3 hours, a recall exam is given with the proportion of correct answers recorded. what type of experimental design is this? a. matched pairb. randomized block designc. surveyd. completely randomized assignmentwhat is the response variable in this experiment? a. the scores on the recall examb. the scores on the pretestc. the ages of the subjectsd. the type of advertisingwhat explanatory variable is manipulated? a. the time before recall examb. the type of advertising