Air pollution has become a major problem nowadays. , Many scientists have made a lot of studies to determine the effects of smog on the lungs., Scientists have discovered more than a hundred elements., For many years, scientists have known that there is no life on the moon., The experiment has ended successfully., We've learned some fundamental ideas about atomic structure., The labeling of the groups of the periodic table has been a matter of some debate among chemists., You can pick up the fungus causing athlete’s foot by wearing shoes that an infected person has worn., AIDS has led to the deaths of more than 25 million people worldwide.,

PRESENT PERFECT - INGLÉS II

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