请解释最后一句英文的语法ButIhadneverdrawnasheep.SoIdrewforhimoneofthetwopicturesIhaddrawnsooften.Itwasthatoftheboaconstrictorfromtheoutside.注：thetwopictures指theboaconstrictorfromtheinside和thebo

Question

请解释最后一句英文的语法
But I had never drawn a sheep.So I drew for him one of the two pictures I had drawn so often.It was that of the boa constrictor from the outside.
注：the two pictures指the boa constrictor from the inside和the boa constrictor from the outside

Answer 1

it was THAT of the boa constrictor..
先忽略 of the outside 之类的
that 可以指代某样东西
that of the boa constrictor..是指那幅画的某样东西