Babies should sleep in their mother's bed until they are at least three years old, which 1 (claim) by a doctor last night.The doctor found that two-day-old babies 2 dozed（打瞌睡）on their mother's chest slept better than those who were placed in cots（婴儿床）.Researchers fear that sleeping alone damages the development of the brain, 3 (lead) to bad behavior as the child grows up.Dr. Nils Bergman, of the University of Cape Town, South Africa, says that for ideal development, healthy newborns should sleep on their mother's chest for the first few weeks. After that, they should stay in the mother's bed 4 they are three or even four years old.Sixteen babies were studied while they 5 (sleep) on their mother's chest and in a cot by her bed. It was revealed 6 the baby's heart was under three times as much stress when he or she slept alone. 7 (be) in a cot also affected sleep, with the babies less likely to make the switch between two types of sleep 8 (call) active and quiet.In the cots, only six out of the sixteen had any quiet sleep and its quality was far 9 (bad).Making this switch is thought 10 (be) the key to the normal development of the brain.

Babies should sleep in their mother's bed until they are at least three years old, which      1      (claim) by a doctor last night. The doctor found that two-day-old babies      2      dozed（打瞌睡）on their mother's chest slept better than those who were placed in cots（婴儿床）. Researchers fear that sleeping alone damages the development of the brain,      3      (lead) to bad behavior as the child grows up. Dr. Nils Bergman, of the University of Cape Town, South Africa, says that for ideal development, healthy newborns should sleep on their mother's chest for the first few weeks. After that, they should stay in the mother's bed      4      they are three or even four years old. Sixteen babies were studied while they      5      (sleep) on their mother's chest and in a cot by her bed. It was revealed      6      the baby's heart was under three times as much stress when he or she slept alone.       7      (be) in a cot also affected sleep, with the babies less likely to make the switch between two types of sleep      8      (call) active and quiet. In the cots, only six out of the sixteen had any quiet sleep and its quality was far      9      (bad). Making this switch is thought      10      (be) the key to the normal development of the brain.