I remember this question myself. If I remember correctly, the answer is C
The key is in D major which means your do will be D (first space under the staff) I will give you the first measure:
Do Do Re Mi
B. Bass as a singing category is pronounced Base.
Answer:
The earliest notated European music was Gregorian Chant. This was a monophonic form of music with all folks contributing their vocal music in 'one voice'. The oldest evidence of this notation comes from around the year 850 and was called the Musica Disciplina of Aurelian of Reome.
Explanation: