Why Was It Difficult for Spanish and Portuguese Mariners to Return

Why was it difficult for Spanish and Portuguese mariners to return home from the Canary Islands?

A) The Northeast Trades, which quickly carried Iberian sailors from the Iberian peninsula to the Canaries, blow steadily southward.
B) Unusual magnetic fields in that area rendered navigational instruments useless.
C) Berber pirates preyed on ships sailing northward from the Canaries.
D) They had no knowledge of the tacking maneuver.