如图示意人体产生屈肘和伸肘动作，请根据图回答下列问题．

    声调是指发音时贯穿于整个音节的高低升降变化。不同的声调分别具有或升或降、或平或曲的变化特点，____。同一个人的不同的音高变化，____。声带越紧，声调越高；声带越松，声调越低。声带先松后紧，声音就由低变高；声带先紧后松，____。控制声带的松紧可以形成不同的音高，从而构成不同的声调。

油漂浮在静止的水面上，说明油的密度____（填“大于”“等于”或“小于”）水的密度；一实心物体刚好能悬浮在水中，将此物体放入足够多的油中时，物体将____（填“漂浮”、“上浮”、“悬浮”或“下沉”）．

Dear Seth,

    You are only three years.old,and at this point in your life you are not able to understand this letter.But some day when you1,I hope you will find something2in what I am going to share with you.

    Life can be3.There will be people in your life who won't be very nice.They'll4you because you are different,5for no good reason.You will also face heartbreak and might be6by those you love.I hope you don't have to face these too much,but such things7.

    Be open to life anyway.You'll find cruelty（残忍）and8n your journey through life,but don't let that9you from finding new things.I don't retreat（退却）from life,and don't10or wall yourself off.Be open to new things,new experiences,and new people.You will11many times,but if you allow that to stop you from trying,you will12 many chances.Do remember failure is a stepping stone to13

    You will meet many people who will try to do14than you,in school,in college,and at work.They'll try to have nicer cars,bigger houses,nicer clothes,and so on.To15,life is a competition.However,I believe life is a16.If you always try your best to17others,you are wasting your life.Learn to enjoy your life18and you will make it a journey of 19of learning and of love.

    Finally,know that I love you and always will.You are20a really wonderful journey,and I will always be there for you.

Love

Dad