American workers in the early 1900s faced several significant challenges. The applicable options from your list include:
- Workers dealt with dangerous working conditions.
- Workers could be exposed to toxic chemicals.
- Workers faced long hours and low pay.
The option about promotion by passing a written test is not a commonly recognized challenge that workers faced broadly during this time period. Therefore, it would not apply as part of the challenges faced by American workers in the early 1900s.