PTE Academic

Dùng mũi tên để đặt các đoạn đúng thứ tự.

1. 1Each course of treatment therefore acts as a form of selection, removing susceptible bacteria and leaving the resistant ones to multiply. The more often a drug is used, the faster this process tends to occur.↑↓
2. 2Antibiotics transformed medicine in the twentieth century, turning once-deadly infections into conditions that could usually be cured within days. For several decades, doctors assumed that this advantage would last indefinitely.↑↓
3. 3Scientists are also searching for new classes of drug, but development is slow and costly, so careful use of existing treatments remains the most practical way to protect their effectiveness.↑↓
4. 4For this reason, health authorities now urge doctors to prescribe antibiotics only when they are clearly needed, and to ask patients to follow the instructions they are given.↑↓
5. 5That assumption proved mistaken. Bacteria reproduce so quickly that any individual carrying a chance mutation allowing it to survive a drug will soon be surrounded by many descendants sharing the same trait.↑↓