Rashi: It is Bi'ah.

Rashi (31, based on Vayikra Rabah 13:5): The coming verse discuss five sets of four matters. They correspond to the four kingdoms that ruled over Yisrael. Because Yisrael transgressed the five Chumashim, this is mentioned five times. She'ol is Malchus Bavel. It says about Nebuchadnetzar "Hirchiv ki'Sh'ol Nafsho" (Chabakuk 2:5). Otzer Rechem is Madai. In their days, they stopped Rachamim (mercy) from Yisrael - "Lehashmid Laharog u'Le'abed" (Esther 3:13).

Malbim (Derech ha'Pashut): [Because they swallowed the poor], they were punished via the rule of Rechem (the king's wives), which increased its desire like She'ol to swallow and destroy. They also received punishments via Hashgachah.

Avodah Zarah 17a: Just like the womb is a place of entry (of seed) and exit (of offspring), the grave is a place of entry (of a Mes) and exit (the dead will be revived). A Kal va'Chomer teaches this -- entry into the womb is done silently, exit is noisy; entry to the grave is noisy (crying and eulogies), all the more so the exit will be noisy! This is a source in written Torah for Techiyas ha'Mesim.

Rashi (31): This is Yavan, which was not satiated from making evil decrees on Yisrael.

Malbim (Derech ha'Muskal): Earth swallows the element of water, with the element of Ru'ach in it, and they constantly convert one to another.

Malbim (Derech ha'Pashut): Rain was withheld; this was punishment of Hashgachah.

Rashi: It is Esav, who acted with burning anger against Yisrael. They wanted to destroy [all men,] children and women in one day ¹ .

Malbim (Derech ha'Pashut): The fourth group was consumed with the entire mouth, just like they consume Aniyim.

Malbim (Derech ha'Pashut): Fire consumed in all their cities; this was punishment of Hashgachah.