Final answer:
Tax treaties do not typically address the issue of tax disclosures made by a visitor to a host country.
Step-by-step explanation:
Tax treaties address various issues related to international taxation. However, the issue of what tax disclosures must be made by a visitor to a host country is not typically addressed by tax treaties. Tax disclosures are usually regulated by domestic tax laws of the host country, rather than through tax treaties.
On the other hand, tax treaties do address issues such as the treatment of business and investment income earned by a foreign visitor in the United States (option b), the treatment of business and investment income earned by a foreign citizen in his home country (option c), and how to compute the taxable amount in the host country (option d).
Therefore, the correct answer is option a. What tax disclosures must be made by a visitor to a host country is NOT addressed by tax treaties.