Final answer:
The best sentence to start a paragraph based on the provided context is a) Many routines are carried out during the school day, as it offers a broad entry point to discuss various aspects of a school's daily operations.
Step-by-step explanation:
The appropriate sentence to begin the paragraph, given the context provided, is option a) Many routines are carried out during the school day. This sentence offers a general and inclusive opener that could lead to discussing various points of a school day, such as structured activities, recess, and impacts on student well-being, attendance policies, and classroom dynamics.
Option b) focuses too narrowly on lessons, option c) is specific to recess activities, and option d) seems disjointed with its mention of teachers grouping, which doesn't clearly connect to routines carried out during the school day.