She is widely seen as proof that good looks can last for ever. But,at nearly 500 years of age, time is catching up with the Mona Lisa.

The health of the famous picture,painted by Lenoardo da Vinci in 1505,is getting worse by the year,according to the Louvre Museum where it is housed.

"The thin, wooden panel on which the Mona Lisa is painted in oil has changed shape since experts checked it two years ago." the museum said. Visitors have noticed changes but repairing the world's most famous painting is not easy. Experts are not sure about the materials the Italian artist used and their current chemical state.

Nearly 6 million people go to see the Mona Lisa every year,many attracted by the mystery of her smile."It is very interesting that when you're not looking at her, she seems to be smiling ,and then you look at her and she stops, "said Professor Margaret Livingstone of Harvard University."It's because direct vision is excellent at picking up detail,but less suited to looking at shadows. Da Vinci painted the smile in shadow."

However,the actual history of the Mona Lisa is just as mysterious as the smile. Da Vinci himself loved it so much that he always carried it with him, until it was eventually sold to France's King Francis I in 1519.

In 1911,the painting was stolen from the Louvre by a former employee,who took it out of the museum hidden under his coat.He said he planned to return it to Italy. The painting was sent back to France two years later.

During World War II, French hid the painting in small towns to keep it out of the hands of German forces.

Like many old ladies,the Mona Lisa has some interesting stories to tell.

1."The health of the famous picture,painted by Lenoardo da Vinci in 1505,is getting worse by the year" means the Mona Lisa ___
A.is losin' its value
B.is bein' damaged after so many years
C.is gettin' more valuable with years passin'
D.will be stolen

2.Experts haven't any repairs on Mona Lisa because ____
A.it's now in a poor chemical state
B.they don't know how to replace the wooden panel
C.they don't have the materials Da Vinci used
D.they are afraid it'll be done further damage

3.The smile of the Mona Lisa can only be seen
A.by indirect vision
B.at a distance
C.by direct vision
D.in shadows

4.From the last paragraph, we can infer that
A.many interesting stories have been written about the Mona Lisa
B.people are interested in the stories about the Mona Lisa
C.Some mysteries still remain to be solved about the mona lisa.
D.many more stories will be told about the Mona Lisa

请在给出选项同时加以解释！

1:B;按照原文的意思是，随着时间的流逝，蒙娜丽沙的画已经慢慢的损坏了；
2:B;他们没有修理是因为他们不知道板的材料和化学性质，从而不知道该怎样替换他；
3:D;第4段最后一句话给出了答案；
4:D,原文讲了几个小故事，1911年被偷，二战期间被藏；最后一个应该是D，
以上是我的理解，有什么不对的地方还请指出来！