Problem: Solar energy may be used in a water stabilisation pond to treat waste water without chemicals or electricity. A further environmental advantage is that algae grow in such ponds and consume carbon dioxide in photosynthesis, although algae may produce toxic chemicals that make the water unusable.
For what reason would solar energy be used in a water stabilisation pond?
The answer is the following: to treat waste water without chemicals or electricity

Problem: In contrast with other Romance languages, Catalan has many monosyllabic words; and those ending in a wide variety of consonants and some consonant clusters. Also, Catalan has final obstruent devoicing, thus featuring many couplets like amic "(male friend") vs. amiga ("female friend").
What other type of endings do Catalan words have?
The answer is the following: consonant clusters

Problem: Parallel with the growth of specialized agencies for conducting or supporting statescraft in the second half of the 20th century has been the collection of resources for scholarship and research typically in university settings. Most universities teaching the liberal arts have library and museum collections. These are not new; however, the erection of these into "centres" of national and international interest in the second half of the 20th century have created larger databases not available to the scholars of the past. Many of these focus on the Ancient Near East or Near East in the sense of Ancient Near East.
What do most universities teaching liberal arts have? 
The answer is the following: library and museum collections

Problem: In July 2013, three former supporters of Mayor Bob Filner asked him to resign because of allegations of repeated sexual harassment. Over the ensuing six weeks, 18 women came forward to publicly claim that Filner had sexually harassed them, and multiple individuals and groups called for him to resign. On August 19 Filner and city representatives entered a mediation process, as a result of which Filner agreed to resign, effective August 30, 2013, while the city agreed to limit his legal and financial exposure. Filner subsequently pleaded guilty to one felony count of false imprisonment and two misdemeanor battery charges, and was sentenced to house arrest and probation.
Why was Mayor Bob Filner asked to resign?
The answer is the following:
allegations of repeated sexual harassment