occur to sb 与it occurs to sb that有什么区别

one genetic mutation(基因突变)occurs on average for every 15 cigarettes that a typical lung-cancer patient smokes, according to a study that has found for the first time all of the mutations happen during the lifetime of a cancer patient.
scientists have completed a full genetic examinations of the genomes（基因组） of cancer patients, and hope the information will lead to a basic understanding of the causes of cancer—and possibly drugs and treatments—by making out the mutations that turn a healthy cell into a cancerous tumor cell.
they studied a lung-cancer patient who had about 23,000 dna mutations in his lung cells that were connected with exposure(暴露) to the toxins found in cigarette smoke and had built up over his lifetime.
they also looked at a patient with malignant melanoma(***黑色肿瘤), the most dangerous form of skin cancer, who had got 30,000 special mutations known to be connected with exposure to sunlight.
scientists believe this new finding into the genetics of cancer will finally lead to new drugs and perfect treatments that aim at the specific changes to the gene that cause the disease, as well as new techniques for discovering following cancers that have escaped from treatment in other parts of the body.
“for the first time, we have a complete map of all mutations in a cancer cell,” said dr. peter campbell, who led the cancer genome project to work out the whole dna system of tumor cells in order find the mutations.
a similar method was performed on the cells of a patient with skin cancer, which is how the researchers were able to show that the malignant skin cells contained changes that resulted from exposure to light.
“these are the two main cancers in the developed world for which we know the chief exposure. for lung cancer it is cigarette smoke, and for malignant melanoma it is exposure to sunlight,” professor campbell said.
小题1:what can the genetic examination of the genomes of cancer patients be used for?

a．to help the professors to win the nobel prizes.

b．to advance the study of reason and cure of cancer.

c．to make the medicine industries earn more money.

d．to help the cancer patients reduce their pain.

小题2:the underlined word in the third paragraph can be placed by_____.

a．smoke

b．sunlight

c．cell

d．poison

小题3:which of the following statements is right according to the passage?

a．the lung-cancer patient had 30,000 mutations in his lung cells.

b．the genetics of cancer will finally lead to new drugs soon.

c．it’s the first time that people mapped mutations in a cancer cell.

d．dr. peter tries to invent a new drug with the dna system.

小题4:what’s the similarity between malignant melanoma and skin cancer of patients?

a．their smoking too much in daily life.

b．their receiving too much sunshine.

c．their refusing to accept treatment.

d．their interest in travelling abroad.

When a disaster occurs, all people, ________ they are old or young, rich or poor, try their best to help those in need.

A．no matter

B．whether

C．however

D．even though