真题演练与解析
最新真题解析（2015年真题）
Directions：In this section there is a passage with ten numbered blanks.For each blank，there are four choices marked A，B，C and D listed on the right side.Choose the best answer and mark the letter of your choice on the
ANSWER SHEET.
A mother who is suffering from cancer can pass on the disease to her unborn child in extremely rare cases， 51 a new case report published in PNAS this week.
According to researchers in Japan and at the Institute for Cancer Research in Sutton，
UK，a Japanese mother had been diagnosed with leukemia a few weeks after giving birth， 52 tumors were discovered in her daughter’s cheek and lung when she was 11 months old.Genetic analysis showed that the baby’s cancer cells had the same mutation as the cancer cells of the mother.But the cancer cells contained no DNA whatsoever from the father， 53 would be expected if she had inherited the cancer from conception.That suggests the cancer cell made it into the unborn child’s body across the placental barrier.
The Guardian claimed this to be the first 54 case of cells crossing the placental barrier.But this is not the case—microchimerism， 55 cells are exchanged between a mother and her unborn child，is thought to be quite common，with some cells thought to pass from fetus to mother in about 50 to 75 per cent of cases and to go the other way about half 56 .
As the BBC pointed out，the greater 57 in cancer transmission from mother to fetus had been how cancer cells that have slipped through the placental barrier could survive in the fetus without being killed by its immune system.The answer，in this case at least，lies in a second mutation of the cancer cells，which led to the 58 of the specific features that would have allowed the fetal immune system to detect the cells as foreign.As a result，no attack against the invaders was launched.
59 ，according to the researchers there is little reason for concern of“cancer danger”.Only 17 probable cases have been reported worldwide and the combined 60 of cancer cells both passing the placental barrier and having the right mutation to evade the baby’s immune system is extremely low.
51.A.suggests B.suggesting C.having suggested D.suggested
52.A.since B.although C.whereas D.when
53.A.what B.whom C.who D.as
54.A.predicted B.notorious C.proven D.detailed
55.A.where B.when C.if D.whateve
56.A.as many B.as much C.as well D.as often
57.A.threat B.puzzle C.obstacle D.dilemma
58.A.detection B.deletion C.amplification D.addition
59.A.Therefore B.Furthermore C.Nevertheless D.Conclusively
60.A.likelihood B.function C.influence D.flexibility
答案及解析
51.【答案】A
【解析】本题考查动词时态。文章第一句为主题句：本周发布的一份新案例研究表明，患癌母亲在极为罕见的情况下，才会将疾病传染给未出生的婴儿。鉴于本题有非常明确的时间状语this week，同时医学权威发布的结果应当为有一定代表性的结论，故选用动词的一般现在时。因此本题正确答案为A。这与第二段中的This suggests
形成正确呼应。
52.【答案】C
【解析】本题考查逻辑关系引导词。本句大意是，一位母亲在分娩的几个月后被诊断为白血病，而女儿在11个月大的时候，在其脸颊和肺部都发现了肿瘤。根据题意，两个分句之间有对比和转折的逻辑关系，因此本题正确答案为C。
53.【答案】D
【解析】本题考查从句引导词。本题的主句结构完整，意思是该女婴癌细胞中未发现父亲的DNA，这就让大家认为她是在受孕过程中染上疾病的。这里需要一个引导词，能指代主句内容，同时还能引导从句，只有as/which才有此功能。因此本
题正确答案为D。
54.【答案】C
【解析】本题考查句意和形容词。本句大意是：《卫报》称这是第一个得以证实的细胞穿透胎盘屏障的案例。上文用一个日本病人的案例对此进行了证明，因此本题正确答案为C。
55.【答案】A
【解析】本题考查逻辑关系和从句引导词。本句大意是：这不是微嵌合状态的病例，在该状态下，细胞在母体和胎儿之间发生交换，非常常见。50%到75%的情况下，一些细胞从胚胎游向母体，50%的情况下则是反向行之。此处从句表示该种情况发生的状态，用where最合适。因此本题正确答案为A。
56.【答案】D
【解析】本题考查副词。这里表示细胞从母亲到胎儿和胎儿到母亲两种方式的几率，能表示“概率，几率，频率”的，只有often。因此本题正确答案为D。
57.【答案】B
【解析】本题考查句意和名词。这里的大意为：这些脱离胎盘的细胞如何不会被免疫系统杀死，这是个令人费解的事情。因此本题正确答案为B。
58.【答案】B
【解析】本题考查句意与名词。对上面提出的puzzle，答案是癌细胞进行了第二次变异，使其能允许免疫系统将其检测为异质的特质消失殆尽。这里只能选择能表示“消失，磨灭”含义的词，才能符合文意。因此deletion是正确答案。
59.【答案】C
【解析】本题考查逻辑关系。这里上文讲的是母体向胎儿传染癌症的情况，空格后则在舒缓对cancer danger的紧张情绪，这是明显的转折关系。因此本题正确答案为C。
60.【答案】A
【解析】本题考查句意和名词。这里进一步解释为何不用担心cancer danger，因为全世界范围内只有17个可能性案例，同时突破胎盘障碍的癌细胞同时避免胎儿免疫系统筛查，两种方式结合起来的可能性实在太低。因此本题选likelihood。