A In the sentence "Water security is the gossamer that links together the web of food" (lines 1 and 2), the word "gossamer" can be correctly replaced bysourcewith no difference in meaning.
B The sentence "The volatility in food prices in 2008 should be treated as an early warning sign of what is to come." (lines 9 and 10) is in the passive voice. In the active voice, it can be written like this:As an early warning sign of what is to come should treat the volatility in food prices in 2008.
C In the fragment "over the past 50 years or so" (lines 15 and 16), the expression "or so" meansin an accurate manner.
D In the sentence "This set of regional challenges becomes a fast-approaching global crisis" (lines 23 and 24), the word "crisis" is in its singular form. In fact, in its plural form, it will showthe same spelling.
E The word "stark", in the sentence "The financial crisis gives us a stark warning" (lines 42 and 43), implies that the financial crisis gives us a complete warning.