Explanation: SITOR (SImplex Teletype Over Radio) uses a 7-unit code for both ARQ (Automatic Repeat reQuest) and FEC (Forward Error Correction) modes, with specific bit patterns serving different functions. The statement in **B) The Idle Signal (a) (0000111) is used for FEC Phasing Signal 1** is correct. In SITOR's FEC mode, two distinct idle signals, Idle Signal (a) (0000111) and Idle Signal (b) (0011001), are continuously transmitted in alternation. These signals, specifically designed with a 3-ones/4-zeros balance, are crucial for the receiving station to establish and maintain character synchronization (phasing) with the transmitting station. Idle Signal (a) serves as Phasing Signal 1. Let's examine why the other options are incorrect: * **A) The Signal Repetition character (1001100) is used as a control signal in SITOR-ARQ.** While 1001100 is indeed the "Repetition Request (RQ)" signal used in ARQ mode, and it *is* a type of control signal, its specific and primary function is to request a retransmission of a block of data. The statement is broadly true, but B describes a more fundamental and precise role within the SITOR FEC synchronization process. * **C) The Idle Signal (b) (0011001) is used for FEC Phasing Signal 2.** This statement is also factually correct, as Idle Signal (b) is indeed Phasing Signal 2 in SITOR FEC. However, in contexts where a single best answer is required, option B (Phasing Signal 1) is often considered the primary or initial phasing signal in the sequence. * **D) The Control Signal 1 (0101100) is used to determine the time displacement in SITOR-B.** Control Signal 1 (CS1) is indeed 0101100 in SITOR. However, its primary function in SITOR-ARQ (SITOR-B) is for call initiation, acknowledgment, and block request, not directly for determining time displacement. While the timing of all signals is used for synchronization, CS1's direct purpose is not "to determine time displacement."