Answer:
Linda assigning people different bowl size is the Independent Variable
Explanation:
Linda is conducting an experimental research , analysing the effect of pasta bowl size on pasta consumption.
The causal variable in a research is an independent variable. And, the variable effected by the independent (causal) variable is the dependent variable.
In this case, pasta serving bowl sizes (quantity) are changed to observe & analyse their impact on amount of pasta eaten by people. Hence :