阅读理解。
It was Mother's Day. John was so busy with his work that he couldn't go back home. When he passed
by a flower shop in the evening, an idea came to his mind."I'll send Mum some roses (玫瑰)."
While John was picking his flowers, a young man went inside."How many roses can I get for only five
dollars, Madam?" he asked. The assistant was trying to tell him roses were as expensive as forty dollars a
dozen (一打). Maybe he would be happy with carnations (康乃馨).
"No, I have to have red roses." He said,"My mum was badly ill last year and I didn't get to spend much
time with her. Now I want to get something special, it has to be roses as rose is her favorite."
After hearing it, John said he would pay the rest of the money for the young man. Moved by both of them,
the assistant said,"Well, lovely young men, thirty dollars a dozen, only for you."Taking the roses, the young
man almost jumped into the air and ran out of the shop. It was well worth twenty-five dollars John paid to see
the exciting moment. Then John paid for his dozen of roses and told the assistant to send them to his mother.
As he walked out, he felt nice. Suddenly he saw the young man crossing the street and going into a park.
But soon he realized it was not a park but a cemetery (墓地). Crying, the young man carefully laid the roses,"
Mum, oh, Mum, why didn't I tell you how much I loved you? God, please help me find my mum and tell her I
love her."
Seeing this, John turned and quickly walked to the shop. He would take the flowers home himself.
1. The assistant tried to ask the young man to buy carnations instead of roses because _______.
A. carnations were nicer than roses
B. roses were saved for John
C. roses were more expensive than carnations
D. carnations were special flowers for Mother's Day
2. John spent _______ altogether (总共) in the flower shop that day.
A. $5
B. $25
C. $30
D. $55
3. The young man cried at the tomb because he _______.
A. had spent all his money on the roses
B. wasn't able to tell his mother he loved her himself
C. felt sorry to ask John to pay for his flowers
D. hadn't got enough money for his sick mother
4. At last John changed his mind and went home because he wanted to _______.
A. tell his mother he loved her himself
B. ask his mother for more money
C. tell his mother the young man's story
D. ask his mother if she liked roses
5. The writer writes the passage to tell us "_______".
A. Buy roses for your mother when she is ill
B. Let your mother know how much you love her
C. Work hard to get more money for your mother
D. Send your mother flowers on Mother's Day
，解得x=1.2m，故B正确；当安培力等于重力时，速度最大，
，解得
，重力最大功率
，故C错误；由能量守恒定律，电阻产生的焦耳热
，故D正确。