1、Unit 4 Section .单词拼写1Astronomy is the scientific study of the sun，the moon ， stars and so on.2The project cost us more than one billion(十亿) dollars.3The atmosphere at home was rather tense.4His fundamental( 根本的) mistake was to rely too much on other people.5Oxygen is a gas that is present in air and
2、 water.6Manmade satellites(卫星) are used for sending and receiving messages.7Anything that is dropped falls towards the centre of the earth because of the pull of gravity(重力)8Global warming and climate (气候) change are perhaps the two greatest threats to our planet.9She was unbelievably gentle(温和的) wi
3、th him during his illness.10A rare virus just attacked my computer system，so it has broken down.选词填空(用方框中所给短语的适当形式填空 ) give birth to， in time， for the first time， lay eggs， in turn1My sister gave_birth_to a lovely baby last night，which made us very happy.2Naturally，you felt nervous when you went on the platform for_the _first_time.3My father told me that not all the animals on the earth produce young by laying_eggs.4We students clean the classroom every day in_turn.5Although we met with some difficulty，we successfully completed the project in_time.
