The correct answer is: B. specify
An employment advertisement should specify the number of vacancies. This is because it is important for potential applicants to know how many positions are available so that they can decide whether or not to apply. Additionally, specifying the number of vacancies helps to ensure that the hiring process is fair and equitable, as all applicants have an equal chance of being selected.
The other options are incorrect because they do not accurately reflect the purpose of an employment advertisement. Option A, “provide,” is too broad, as an employment advertisement can provide a variety of information, such as the job title, description, and qualifications. Option C, “contain,” is also too broad, as an employment advertisement can contain a variety of information, such as the company’s name, address, and contact information. Option D, “declare,” is incorrect because an employment advertisement does not declare anything. It simply provides information about a job opening.