Which of the underlined words in the sentence is INCORRECT? To become a teacher and to helping children learn English is…

The Food Science book was very short. It didn't have ...................... chapters.

Reaching the summit of the mountain was ......... challenge of Ali's life.

Children are welcome to join us on our next trip ...... they behave themselves.

Mr. Amir, --------------- the students call Uncle Amir, taught the boys physical education several times a week.

… ............... the new iPhone was so expensive, George bought it because he loved the design.