My sister failed the exam because she was lazy. → Because of .....
Giải thích
Because of my sister’s laziness, she failed the exam. /Because of her laziness, my sister failed the exam. /Because of being lazy, my sister failed the exam.
Because of my sister’s laziness, she failed the exam. /Because of her laziness, my sister failed the exam. /Because of being lazy, my sister failed the exam.