请教0001语法找错29,39

the orbit of a celestial body is usually in the shape of ellipse

the answer ,d,but  why ?

lowell,massachusetts,known as the "spindle city"since 1882 when the first textile mills were built ,atrracted worldwhile attentions as textile center.

the answer,d,   it should be "as a textile "?????

thanks...

29. ellipse前面加an

39. agree with you