Concept:A rak'ah is one complete unit of the Muslim prayer (salat), and it begins with the opening Takbir.
Explanation:Salat is made up of repeated units called rak'ahs, and each unit begins with Takbiratul Ihram.
Takbiratul Ihram is the opening declaration of "Allahu Akbar" that formally marks the start of the prayer.
After this Takbir, the worshipper stands to recite Surah Al-Fatihah, then moves to Ruku (bowing), returns to the standing position (Qiyam bi Itidal), and finally performs Sujud (prostration).
Since Ruku, Sujud, and Qiyam bi Itidal all come later in the sequence, none of them can be the starting act.
Therefore, the prayer and its first rak'ah are both initiated by Takbiratul Ihram.
Answer:A. Takbiratul Ihram