The correct choices are:
1. Caribbean colonies were used as a base to conquer the mainland;
2. Malinche helped the Spanish ally with Aztec enemies;
4. A battle broke out between the Aztecs and the Spanish in which Moctezuma was killed;
The Spanish initially conquered islands in the Caribbean region. They used them as basis for expeditions and conquering on the mainland at first. When the Spanish arrived on the mainland, they encountered the Aztecs, and they were actually welcomed and treated very nicely. The Spanish though, wanted to get the Aztec's riches, so they started allying with the tribes that hated the Aztec rule. Together, the Spanish and the local tribes attacked the Aztecs, and managed to conquer their capital Tenochtitlan, killing their leader Moctezuma in the process.