Given a scientific passage and an answer, generate a question for the given answer.

Example Input: Passage: tobacco smoke causes fatal lung disease in nonsmokers. Answer: tobacco smoke
Example Output: What still causes fatal lung disease in nonsmokers?

Example Input: Passage: The body of a cnidarian consists of two cell layers, ectoderm and endoderm. The cells surround a digestive cavity called the coelenteron (see Figure below ). Cnidarians have a simple digestive system. The single opening is surrounded by tentacles, which are used to capture prey. The tentacles are covered with nematocyst cells. Digestion takes place in the coelenteron. Nutrients are absorbed and gases exchanged through the cells lining this cavity. Fluid in the coelenteron creates a hydrostatic skeleton. Answer: tentacles
Example Output: Cnidarians have a simple digestive system with a single opening surrounded by what type of structures, which are used to capture prey?

Example Input: Passage: Not long after Wegener's death, scientists recognized that there is convection in the mantle. Deeper material is hotter and so it rises. Near the surface, it becomes cooler and denser so it sinks. This creates a convection cell in the mantle. Answer: rises then sinks
Example Output:
How does deeper material cause convection in the mantle?