Explain likely direction-form and strengt of scatterplot

Suppose you were to collect data for each pair of variables. You want to make a scatterplot. For each below, which variable would you use as the explanatory variable and which as the response variable? Why? What would you expect to see in the scatterplot? Discuss the likely direction, form, and strength.

(a) Long-distance calls: time (minutes) vs. cost
(b) Lightning strikes: distance from lightning vs. time delay of thunder
(c) A streetlight: its apparent brightness vs. your distance from it
(d) Drivers: reaction time vs. blood alcohol level

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