Which thesis statement is strong because it demonstrates confidence?

a.)$.)$

I feel that the unsanitary living conditions of the urban poor in the early 20$20$th century contributed to the high infant mortality rate of the time.

b.)$.)$

The main reasons for the high infant mortality rate in the early 20$20$th century were government corruption and unsanitary housing.

c.)$.)$

It's possible that if city governments had better enforced existing housing and sanitation laws in the early 20$20$th century, the infant mortality rate would have been lower.

d.)$.)$

I believe that the infant mortality rate in the early 20$20$th century was negatively affected by overcrowding in cities and a lack of access to healthcare.