Conflicts over toilet training, and other attempts by a 2-year-old to exert control over his or her environment, are most evident during the stage of psychosexual development.

These are most evident during the an al stage of psychosexual development.

Explanation:

According to Freud, there are 5 psychosexual stages every individual goes through throughout his/her life.

Key factors about the an al stage:

It occurs around 18 months of age- 3 years old. This is the stage where a child learns about exerting control by controlling his/her sphincters; this is because hi/her parents depend on him/her and his/her potty training. A fixation during this stage tends to relate to hoarding in later years, which refers to extreme accumulation of something. It can also relate to an extreme organization and could develop into OCD, for example.

Ithink the answer you are looking for is (b).