He sitting at the back of the classroom and his eyes staring at the blackboard.是錯(cuò)誤的.
前后兩部分全是ing形式的現(xiàn)在分詞,是非謂語動(dòng)詞,所以整個(gè)句子缺少謂語.
Sitting at the back of the classroom,his eyes stared at the blackboard.
這個(gè)就完全正確.
Sitting at the back of the classroom是現(xiàn)在分詞做狀語
后面的his eyes stared at the blackboard已經(jīng)是一個(gè)完整的句子了,主謂賓俱全.
可以寫成這樣,也是正確的：He is sitting at the back of the classroom,his eyes staring at the blackboard.
這就變成了He is sitting at the back of the classroom是一個(gè)完整的句子
his eyes staring at the blackboard是現(xiàn)在分詞做狀語
或者直接用and連接兩個(gè)并列句,也是正確的：
He is sitting at the back of the classroom and his eyes are staring at the blackboard.
這樣的話,and前后都是完整的句子.