Today, research that combines an experimental strategy with __________ approach is becoming increasingly common.

The blank in the statement refers to an approach that can be used in combination with an experimental strategy. Longitudinal and cross-sectional approaches are two common research methods in developmental psychology. Longitudinal studies involve following the same group of individuals over an extended period, while cross-sectional studies compare different groups of individuals of different ages at the same time. By combining an experimental strategy with either a longitudinal or a cross-sectional approach, researchers can gain a deeper understanding of developmental processes and changes over time. Choices A, B, and D are incorrect because correlational and sequential are not the most relevant approaches when studying developmental changes over time in research.