"a. After the rain ended, the sky became blue" would contain an independent clause and a dependent clause, which makes it a complex sentence, since the latter half wouldn't be the same without the former half.
Mar 1, 2013 - <span>Sections are divided </span>into<span> general tips for varying structure, a discussion of </span>sentence types<span>, and specific parts of speech which </span>can<span> aid in </span>sentence variety<span>. ... </span>1<span>. Vary the rhythm by alternating </span>short<span>and </span>long sentences<span>. </span>Several sentences<span> of the </span>same length can make<span> for bland </span>writing<span>. To enliven paragraphs </span>