In a 2017 study designed to investigate the effects of exercise on second language learning, 40 subjects were randomly assigned to one of two conditions: an experimental group that engaged in simultaneous physical activity while learning vocabulary in a second language and a control group that learned the vocabulary in a static learning environment. Researchers found that learning second-language vocabulary while engaged in physical activity led to higher performance than learning in a static environment. Liu et al., “It takes biking to learn: Physical activity improves learning a second language,” PLoS One, May 18, 2017, https://doi.org/10.1371/journal.  pone.0177624

a. What features of a well-designed controlled experiment does this study have? Which features are missing?

b. Assuming that the study was properly conducted, can we conclude that the physical activity while learning caused the higher performance in learning second-language vocabulary? Explain.