Elizabeth wouldn't walk or talk as an infant.Angela's left leg was so enlarged that it hurt to stand.Emma needed a breathing machine just to sleep.Their suffering may take different forms，but their stories share a common thread：Neither they nor their families knew what was actually causing these issues.
   Undiagnosed diseases are more common than you might think.Tens of millions of Americans likely suffer from disorders they cannot name.For many，the symptoms are minor.But in some cases，patients come to their doctors with serious problems caused by diseases that challenge medical knowledge.
   Those cases are precisely where the Undiagnosed Diseases Network（UDN）steps in.Established in 2008，the UDN's mission is to provide answers for patients with diseases that doctors are unable to diagnose.Anyone can apply to the program and the UDN works hard to screen every application it receives.
   Today，the UDN covers 12 clinical sites around the country，and has evaluated over 1，400 patients.More than 400 of those patients have received a diagnosis thanks to the UDN.In some of these cases，the network is able to match a patient with an already known condition.In others，UDN researchers must work to describe an entirely new disease and enter it into the medical dictionary.The program has added at least 25 entirely new diseases in this way.Additionally，the UDN covers the cost of the tests，meaning patients aren't burdened with crushing medical debt.
   This kind of groundbreaking work helps more than just the patients themselves.Insights from studying rare diseases offer new knowledge about the human body that can benefit all of us.For example，the discovery of statins，a class of drugs commonly recommended today to help regulate high blood pressure，arose from the study of a rare genetic disorder.
   "I think they've really advanced and changed the whole model for how we approach many of these illnesses，" says Anne Pariser，director of the Office of Rare Diseases Research.She says the UDN's multidisciplinary approach - bringing different specialists together to talk about challenging cases -has helped advance the field of rare disease research，especially when it comes to genetic diseases.
   Living with a disease without a name can be its own kind of suffering. "You grow up feeling like，I'm in this，crazy，all by myself，and no one really understands me，" says Angela Moon，a UDN participant.For patients like her，the UDN offers hope for treatment，but also for finally being seen.

（1）The purpose of the first paragraph is to

C

C

.
A．a(chǎn)rouse the readers' interest in the UDN
B．give a vivid description of rare diseases
C．introduce the background for the UDN's founding
D．raise a complicated problem that will be solved later
（2）The fourth paragraph mainly talks about

B

B

.
A．the way the UDN is operated nationwide
B．the progress the UDN has made so far
C．the reasons why the UDN is so popular
D．the development stages the UDN has gone through
（3）What can be learned about Angela Moon？

A

A

A．She used to live in despair.
B．She failed to identify with others.
C．She is receiving treatment now.
D．There will be a cure for her condition.
（4）What can be inferred about the UDN's work model？

D

D

A．It has helped spread the knowledge of undiagnosed diseases.
B．It prioritizes participants' privacy over solving medical mysteries.
C．It is specifically designed to deal with challenging genetic diseases.
D．It emphasizes close cooperation between specialists in separate fields.