∫ The quadrilateral ABCD is a diamond.
∴AB=AD,∠ABC=∠ADC
AE = AF = EF = AB
That is, AB=AE and AD=AF.
∴ ∠ABC=∠AEB，∠ADC=∠AFD
∠ABC=∠AEB=∠ADC=∠AFD
AB = AD
∴△ABE≌△ADF
∴∠BAE=∠DAF
∠ABE=( 180 degrees -∠BAE)/2
∫∠ABE+∠BAD = 180 degrees
∴∠ABE+∠BAD=( 180 degrees -∠BAE)/2+∠BAE+FAD+60 degrees =( 180 degrees-∠ BAE)/2+
∴90 degrees -2/3∠BAE= 120 degrees, ∠BAE=20 degrees
∴∠C=∠BAD=2∠BAE+60 degrees =20 degrees *2+60 degrees = 100 degrees.
A: The degree of angle C is 100 degrees.