S4. The students’ exams, grades and marks should only be estimated by______.

A．A comparison of jogging and other exercises.
B．A discussion of jogging as a physical fitness program.
C．A description of the type of clothing needed for jogging.
D．Providing scientific evidence of the benefits of jogging.

A．Find a quiet place to study.
B．Change the conditions of his room.
C．Find a more comfortable place to study.
D．Avoid distractions while studying in his room.