Use $\_\_\_\_\_\_\_\_$ headings for any subsections within the introduction of a paper.

a$.$

Level $4$

b$.$

Level $1$

c$.$

Level $3$

d$.$

Level $2$Use $\_\_\_\_\_\_\_\_$ headings for any subsections within the introduction of a paper.

a$.$

Level $4$

b$.$

Level $1$

c$.$

Level $3$

d$.$

Level $2$Use $\_\_\_\_\_\_\_\_$ headings for any subsections within the introduction of a paper.

a$.$

Level $4$

b$.$

Level $1$

c$.$

Level $3$

d$.$

Level $2$