Most studies ____ that acupuncture does not reduce nausea and vomiting

Most studies ____ that acupuncture does not reduce nausea and vomiting caused by radiation therapy.

• A. are shown
• B. were shown
• C. have shown
• D. have been shown

bị động với các động từ chỉ quan điểm, ý kiến:  S1 + V1  + THAT + S2 + V2 +…..