Read the following passage about heart attacks and mark the letter A, B, C, or D on your answer sheet to indicate the option that best fits...

Read the following passage about heart attacks and mark the letter A, B, C, or D on your answer sheet to indicate the option that best fits each of the numbered blanks from 18 to 22.

        Mounting evidence shows that more young adults are experiencing heart problems than in previous decades. Heart attacks occur when blood flow to the heart (18) ____________. One reason is the growing number of lifestyle-related health problems, (19) ____________. Other factors like tobacco, cocaine, marijuana, and alcohol use have been associated with increased risks of heart attack in younger adults too.

The major risk factors—high blood pressure, high cholesterol, diabetes, and obesity—can damage arteries over time. While these conditions may be inherited, (20) ____________ often play a larger role.

        (21) ____________. A recent survey found that 47% of people under 45 don’t believe they’re at risk for heart disease, and one-third of adults wouldn’t confidently recognize heart attack symptoms. Half of 3,500 younger adults with significant risk factors didn’t believe they were at risk before their heart attack occurred. Even fewer said their doctors warned them—especially women.

        Experts say that getting young adults to care about heart health is a unique challenge. (22) ____________. Experts emphasize early prevention, since untreated risk factors lead to worse outcomes over time.

(Adapted from National Geographic)

Question 18. 

        A. is partially or completely blocked                        B. that is partially or completely blocking

        C. is getting a blockage completely                        D. has been incompletely blocked