How to create dependent drop downs on form

I am nearly finished with an incident investigation report form, but would like to include dependent drop down menus so that we can assist users in identifying the root cause once they have selected the basic cause.

As an example, if they have determined that the Job/System Factor basic cause is Inadequate Leadership and/or Supervision, I would like the next available drop down menu to be options to be limited, like Unclear or conflicting reporting relationships or Unclear or conflicting assignment of responsibility. Or, if they were to select Inadequate Engineering as the basic cause, the root cause options would only include Inadequate assessment of loss exposures, or Inadequate consideration of human factors/ergonomics, and no longer be able to select Unclear or conflicting relationships.

So basically, the first drop down will have options for the basic cause, to include: Inadequate Physical/Physiological Capability, Inadequate Mental/Psychological Capability, Physical or Physiological Stress, Mental or Psychological Stress, Lack of Knowledge, Lack of Skill, Improper Motivation, Abuse or Misuse, Inadequate Leadership and/or Supervision, Inadequate Engineering, Inadequate Purchasing, Inadequate Maintenance, Inadequate Tools and Equipment, Inadequate Work Standards, Excessive Wear and Tear, and Inadequate Communications.

Then, there will be a second drop down for the root cause that will have a specific set of options that appear depending on what they have selected as the basic cause.

This will be based on the SCAT basic/root causes.

I have tried to set this up but must be inputting improper script (I am clearly not even remotely versed in java script) or in the improper area.

Any assistance would be greatly appreciated!