Another solution is to use the plain enum (or list) functions.
#set par(first-line-indent: 1em, justify: true, leading: 1em)
#show par: set block(spacing: 1em)
#lorem(25)
#lorem(25)
#enum(
numbering: "1.a)", indent: 1em,
enum.item[Lorem ipsum dolor sit amet.],
enum.item([Lorem ipsum dolor sit amet.] + enum(
numbering: "1.a)",
enum.item[Lorem ipsum dolor sit amet.],
enum.item[Lorem ipsum dolor sit amet.]
))
)