It is believed that modern farming methods have greatly improved farmers’ lives.
A. Farmers are believed to have enjoyed a much better life thanks to modern farming methods.
B. Modern farming methods were believed to have greatly improved farmers’ lives.
C. Modern farming methods are believed to have had negative effects on farmers’ lives.
D. People believe that there is little improvement in farmers’ lives thanks to modern farming methods.

Thầy Duy giải thích giúp em là đáp án là B nhưng em thấy thì trong câu B là quá khứ đáng ra phải là hiện tại chứ ạ. Em cảm ơn thầy!