Chaitanya Mahaprabhu’s philosophical thoughts and teachings are collected in a book called _____________.
A.Chaitanya Charitamrita
B.Guru Grantha Sahib
C.Bijak
D.Puranas

Hint: Let's discuss about the Chaitanya Mahaprabhu’s philosophical thoughts and teachings, so Chaitanya was born in Nabadwip (current West Bengal) on 18 February 1486, Shri Krishna Chaitanya Mahaprabhu was a Indian saint and founder of Achintya Bheda Abheda during 15 century. It is also said he is the incarnation of the God Krishna.

Complete answer:
Chaitanya ideas and thoughts are collected in a book named 'Chaitanya Charitamrita' by Krishna Das Kaviraja in Bengali Language with Sanskrit verses. The Chaitanya Charitamrita is split into 3 sections: Adi-lila, Madhya-lila and Antya-lila. All the sections are referred to his life, those are:
A. Adi-lila
The Adi-lila explains Chaitanya's distinctive system of rules identity (Krishna within the mood of Radharani—a combined avatar), his lineage, his nearest childhood companions and their lineage, and his pious associates. It ends with a quick outline of his life up to his acceptance of sannyasa.
B. Madhya-lila
The Madhya-lila details Chaitanya's sannyasa; Madhavendra Puri's life; Chaitanya's philosophical oral communication with Sarvabhauma Bhattacharya (Advaitin scholar) promoting devotion as supreme over the impersonal view; Chaitanya's journey to South India; the daily and annual activities of Chaitanya and his devotees throughout the Ratha Yatra competition close to Jagannath Temple (Puri, Odisha); their observance of alternative festivities; and Chaitanya's directions on the method of devotion yoga to each Rupa Goswami and Sanatana Goswami.
C. Antya-lila
The Antya-lila describes the pious plays composed by Rupa Goswami, Chaitanya's interactions with the occasional critics moreover as his devotees like Raghunatha dasa Goswami and Jagadananda Pandita, and Chaitanya's increasing agony of separation from Krishna (viraha or vipralambha bhava). It concludes with the Chaitanya's Shikshashtakam (eight verses of poetic instruction).

Hence, the correct answer is option (A).

Note: Chaitanya introduced the mass of individuals within the Sankhya philosophy of “Achintya bhedabheda” that maintain that the supreme God is at the same time one with and totally different from his creation. He instructed that the holy name of God is that of the sound incarnation of God.