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

Ex Input:
Passage: The strong nuclear force works only over very short distances. As a result, it isn't effective if the nucleus gets too big. As more protons are added to the nucleus, the electromagnetic force of repulsion between them gets stronger, while the strong nuclear force of attraction between them gets weaker. This puts an upper limit on the number of protons an atom can have and remain stable. If atoms have more than 83 protons, the electromagnetic repulsion between them is greater than the strong nuclear force of attraction between them. This makes the nucleus unstable, or radioactive, so it breaks down. The following video discusses the strong nuclear force and its role in the atom. The video also introduces the weak nuclear force, which is described next. Answer: unstable, or radioactive

Ex Output:
If the electromagnetic repulsion between protons is greater than the strong nuclear force of attraction between them, what do they become?

Ex 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

Ex Output:
Cnidarians have a simple digestive system with a single opening surrounded by what type of structures, which are used to capture prey?

Ex Input:
Passage: Figure 21.14 Vaccinations are designed to boost immunity to a virus to prevent infection. (credit: USACE Europe District). Answer: infection

Ex Output:
Vaccinations are designed to boost immunity to a virus to prevent this?