Explanation: To qualify for a Third Class Radiotelegraph Operator's Certificate, an applicant must demonstrate proficiency in both written knowledge and Morse code reception. **Option A is correct** because it accurately describes these requirements. The "appropriate written examinations" refer to FCC Elements 1 and 3, covering basic radio law, operating procedures, and general radiotelegraphy practices. The crucial component is the Morse code receiving examination, where the applicant must accurately receive (by ear) code groups at 16 words per minute and plain text at 20 words per minute for a period of one minute without error. This tests the applicant's ability to interpret telegraphic signals. **Option B is incorrect** because sending radiotelegraphy is not a requirement for any FCC radiotelegraph operator certificate, and there is no age requirement of 21 years old for this certificate. **Option C is incorrect** because it only mentions written examinations (Elements 1 and 3, though it incorrectly states Element 2 here, which is the code test element for Second Class) and completely omits the mandatory Morse code receiving requirement. **Option D is incorrect** because while it includes both written examinations and a telegraphy receiving examination, Option A provides a more specific and accurate description of the code test's format, including receiving code groups and plain text for a minute without error, which are key details of the FCC's testing standards for this certificate.