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

Passage: The Arrhenius definition of acids and bases is somewhat limited. There are some compounds whose properties suggest that they are either acidic or basic, but which do not qualify according to the Arrhenius definition. An example is ammonia (NH 3 ). Its aqueous solution turns litmus blue, it reacts with acids, and displays all the other properties of a base. However, it does not contain the hydroxide ion. In 1923, a broader definition of acids and bases was independently proposed by Danish chemist Johannes Brnsted (1879-1947) and English chemist Thomas Lowry (1874-1936). A Brnsted-Lowry acid is a molecule or ion that donates a hydrogen ion in a reaction. A Brnsted-Lowry base is a molecule or ion that accepts a hydrogen ion in a reaction. A hydrogen ion is commonly referred to as a proton, and so acids and bases are proton donors and proton acceptors respectively according to the Brnsted-Lowry definition. All substances that are categorized as acids and bases under the Arrhenius definition are also defined as such under the Brnsted-Lowry definition. The new definition, however, includes some substances that are left out according to the Arrhenius definition. Answer: acid
Which type of substance is considered a proton donor in a reaction?

Passage: Leaves, Sporophylls, and Strobili A third innovation marks the seedless vascular plants. Accompanying the prominence of the sporophyte and the development of vascular tissue, the appearance of true leaves improved their photosynthetic efficiency. Leaves capture more sunlight with their increased surface area by employing more chloroplasts to trap light energy and convert it to chemical energy, which is then used to fix atmospheric carbon dioxide into carbohydrates. The carbohydrates are exported to the rest of the plant by the conductive cells of phloem tissue. The existence of two types of morphology suggests that leaves evolved independently in several groups of plants. The first type of leaf is the microphyll, or "little leaf," which can be dated to 350 million years ago in the late Silurian. A microphyll is small and has a simple vascular system. A single unbranched veina bundle of vascular tissue made of xylem and phloemruns through the center of the leaf. Microphylls may have originated from the flattening of lateral branches, or from sporangia that lost their reproductive capabilities. Microphylls are present in the club mosses and probably preceded the development of megaphylls, or "big leaves", which are larger leaves with a pattern of branching veins. Megaphylls most likely appeared independently several times during the course of evolution. Their complex networks of veins suggest that several branches may have combined into a flattened organ, with the gaps between the branches being filled with photosynthetic tissue. In addition to photosynthesis, leaves play another role in the life of the plants. Pine cones, mature fronds of ferns, and flowers are all sporophyllsleaves that were modified structurally to bear sporangia. Strobili are cone-like structures that contain sporangia. They are prominent in conifers and are commonly known as pine cones. Answer: strobili
What are the cone-like structures that contain sporangia called?

Passage: Zinc reacting with hydrochloric acid produces bubbles of hydrogen gas. Answer: hydrogen
Zinc reacting with hydrochloric acid produces bubbles of which gas?