Under Public Law 86-272, which of the following actions by itself would create income tax nexus for a taxpayer with a state?

a. Maintenance of the taxpayers inventory in the state by an independent contractor to be used for deliveries to customers in the state.

b. Having a sales employee who is a resident of the state, but who performs services only in another state.

c. Using an independent contractor who acts as sales agent for the taxpayer through the contractors sales office in the state.

d. Shipping tangible personal property it sells to residents of the state from its warehouse located in another state.

e. Executing a sales campaign, using an advertising agency acting as an independent contractor for the taxpayer.