Passage 3: Questions 29-32        Over the last decade, the field of cell therapy has expanded rapidly. While some forms of celltherapy, such as hematopoietic stem cell transplantation to treat certain types of cancer, have been knownfor a while, it has only been in recent years __(29)__ the field has really started to expand.       Cell therapy holds enormous promise for treating genetic diseases, cancer, and autoimmunedisorders. However, there are still some teething problems that need to be __(30)__ . Cells arebiological material and notoriously unpredictable to grow and transport. Setting up a reliable, consistentand scalable manufacturing system is key to producing cell therapy on a wider scale. If this problem canbe cracked, then the issue of excessively high pricing currently __(31)__ a mass rollout might also beat least partly solved. Last but not least, ensuring these therapies are safe for patients and adequatelyregulated is __(32)__.
【題組】29.
(A) as
(B) how
(C) that  
(D) while