11. It is because people are likely to stay indoors the virus can spread easily people o

问题补充：

11. It is because people are likely to stay indoors the virus can spread easily people often catch colds.

A. and, that

B. so, that

C. therefore, so

D. that, that

答案：

A. and, that

B. so, that

C. therefore, so

D. that, that

解析：