Why was it very difficult for foreign students to study at Vietnamese universities?

Read the passage about international students in Viet Nam, and then answer the questions.

Viet Nam is changing university enrolment requirements to make it easier for foreign students to study at its universities. Previously, foreign students were required to take university entrance examinations in Vietnamese, making it difficult if not almost impossible for non-Vietnamese-speaking foreign students to apply.

International student enrolment is one of the criteria to rank Vietnamese universities. Attracting foreign students is also a way for Vietnam to promote Vietnam's education to the world.

The leading universities in Viet Nam enrol undergraduate and graduate international students every year. Most are from the Asia Pacific region including China, Japan, Korea, Australia, Laos, Cambodia and Thailand, while a few come from the United States and Europe. Most of the international students study Vietnamese studies, Vietnamese literature or South East Asian studies, which makes Viet Nam the best destination for them.

The leading institutions such as Viet Nam National Universities in Ha Noi and Ho Chi Mirth City, which have a tradition of hosting international students, run preparatory courses in Vietnamese for foreign students. However, it's widely recognized that if these universities do not have programmes taught in English, they have a challenge to enroll international students.

Why was it very difficult for foreign students to study at Vietnamese universities?

• A. Because they were required to take university entrance examination in Vietnamese 
• B. Because they didn't need to take university entrance examination in Vietnamese 
• C. Because they were forced to take university entrance examination in Vietnamese 
• D. Because they were required to take university entrance examination in English