The layers of the digestive tract go to in this order (starting from the lumen).
a. submucosa, mucosa, serosa, muscularis
b. mucosa, muscularis, serosa, submocosa
c. muscularis, serosa, mucosa, submucosa
d. mucosa, submucosa, muscularis, serosa

d. mucosa, submucosa, muscularis, serosa

Explanation:

The layers of the digestive tract starting from the lumen are mucosa, submucosa, muscularis and serosa.

The first layer is mucosa which is made of epithelium cells and helps in absorption of nutrients from digested food. It has numerous villi structure which increase the surface area for absorption. Second layer submucosa supports mucosa and is supplied with large blood vessels, nerves and lymphatics. Absorbed nutrients enter the blood vessels which are present in submucosa. The third layer muscularis functions to create peristaltic movements in GI tract. Muscles in this layer make the food move and mix with digestive juices. Final layer serosa works to reduce friction between digestive tract muscles. It has a thin cell layer which secretes serous fluid that acts as a lubricant.

Leaves specifically the gas exchange between plants and the environment. while plants undergo photosynthesis, they also partake in cellular respiration. respiration is the process that happens in the leaves of plants.