More than ___________ compounds of tar of tobacco smoke are involved to cause cancer?

Explanation

The question uses the conventional textbook figure that more than 10 compounds in tobacco tar contribute to cancer, so option d is intended. These carcinogenic substances can damage DNA and promote uncontrolled cell division. Students may choose 90 because tobacco smoke contains many harmful chemicals overall, but that is not the specific figure stated for the carcinogenic tar compounds in this syllabus.