Answer:
a) ∠CFB, ∠BFA
Explanation:
Acute angles are angles < 90°
AD is a straight line
⇒ ∠CFD + ∠CFB + ∠BFA = 180
⇒ 90 + ∠CFB + 50 = 180
⇒ 140 + ∠CFB = 180
⇒ ∠CFB = 180 - 140
⇒ ∠CFB = 40
∠CFB and ∠BFA are adjacent angles
∠CFB = 40
∠BFA = 50
Both are less than 90°
∴ ∠CFB and ∠BFA are adjacent acute angles