It would be "interesa".
A nosotros nos "interesa" jugar al baloncesto.
What situation are you referring to?
The answer is
La revista Cosas es mi favorita. ___La compro_________ todos los meses.
The female and singular pronoun <u>La </u>is replacing the magazine (revista Cosas) which in Spanish is also female.
the other options do not apply because:
<u>Lo</u> compro is male gender
<u>Las</u> and <u>los</u> are for plural and the sentence states only one magazine.
