one possible version:
june 8, 20xx dear sir, i'm sorrto tell you that i can't go to school today, i've caught a cold because i swam in the school'swimming pool yesterday. thimorning i had a headache. after taking mtemperature, mmother found that i had a high fever, immediatelshe took me to see a doctor, who advised me to stain bed for 2 days. now i am writing to you to ask for 2 days' sick leave. with best wishes.
your student,
tom
Dear Mr/Ms Wang
I was unable to come to 1st and 2nd period today.Due to the rain yesterday, I was wet and had temperature at night. The doctor adviced me to rest for several days and after my recovery, I will attend school as soon as possible.
I am sincerely sorry about the inconvenience. However, I would like to have your permission. Also, afterwards I would phone you and there's the certificate by the doctor.
Li Tie
October 21st 20xx
Dear Mr. xx,
I'm sorry to tell you that I caught a cold and I'm not feeling well now.I am adviced to stay in bed for two days and can't go to school then.But I think I'll get well soon and be back the day after tomorrow.
Yours sincerely,
xx
20xx年x月x日
dear teacher:
i'm sorry i have to ask for two daysoff. because i had a bad cold yesterday. and now i have a high fever.
i am feeling very bad.i can't study freely in class 。i went to see a doctorin the hospital.he gave me some medicine and asked me to stay in bed for two days 。so i'm sorry to ask you two days leave. i hope you can ratify my ask. thank you very much.
yours， sam
Dear Sir or Madam:
Dear Mr Li/Miss Li/Mrs Li,I beg to apply for two days’ leave/a week’s leave/7 days’ leave of absence（请假）from the 7th to 8th of this week. Because I was ill, I want to return/go home to see the doctor.
To support my application, I herewith/enclose the sick leave certificate.
I should be very much obliged if you will grant me my application. As regards the lesson to be missed during my absence, I will do my best to make them up as soon as I get back from leave.
Yours respectfully,
Li Min
teacher wang:
today， because of my grandmother was seriously ill， with parents to visit， ask for leave one day.
sincerely yours
salute!
student: li binbin
x dated
1 March, 200
Dear Director,
I beg to apply for one’s week’s leave of absence from the 1st to 7th instant, both days inclusive, in order to return home to see my grandfather, who is now serious ill. To support my application, I herewith submit the telegram received from my father last night.
Respectfully,
James Smith
instant本月的（略作 inst.）： your letter of the 28th instant您本月二十八日的来函
尊敬的主任：
因祖父病重，欲回家探望。申请事假一周，从本月一日起到七日止。附上昨晚收到的家父电报，以资证明。
致
礼！
詹姆斯·史密斯
范文六(asking for sick leave)
Dear Mr. Wang,
I am very sorry that I shall be unable to come to your classes today owing to a bad cold. I enclose a certificate from the doctor who is attending me. He said it will be two or three days before I shall be able to resume my school.
David
April 20
王老师：
很抱歉，我因患重感冒今天不能到校。现附上医生证明，他说我两三天后才能到校学习。
大卫
四月二十日
Dear Sir/Madam,
I caught a cold and I'm not feeling well now.I am afraid I have to stay at home for two days,since the doctor ask me to have more rest.
Regards,
xxx
To: John Smith, Supervisor
From: George Chen, Accounting Department
Date: March 11, 20xxSubject: Casual Leave of Absence
John, I would like to know if I could ask for a casual leave of absence from March 23 to 27.
Yesterday I received a letter from my parents, who are both over 70, telling me that a big flood took place at my home village, causing serious damage to my house. As the only son of my parents, I should of back to assess the situation, and help them to get over these difficulties. Though I cannot stay at home for too long a time, I should at least make arrangements for repair work. I believe my relatives in the village and my neighbors will also come to help. Financially I have no difficulties.
I will call you at 1:30p.m. or you can call me at any time.
Dear Mr. XX,
I want to ask for leave this Friday. Because I always cough recently, I need a doctor. Besides, I almost finished my work this week. I will call the manager when I go to see the doctor. Please allow me to ask. Thank you.
Jackson
September 14th, XX