(A number) of these (who) (study) engineering is improving (steadily).
【正确答案】 A
【答案解析】应改为the number of 。 the number of sth.表“……的数量”,做主语时,谓语动词用单数形式,而the number of表“许多,很多”时,后面加可数名词复数做主语,谓语动词用复数形式