Today's production of biofuels derived from corn or from palm oil crop

I would say so, achloes. In fact, I came up with the same idea when I saw answer choice (C). Just because one plant yields less oil does not mean the oil extracted from each plant is equally usable. I would also say that gmatophobia brings up an excellent point above: we have no information in (C) about the type of land on which each plant is grown, so an acre-to-acre comparison might not be meaningful.

Thank you for thinking to ask, and good luck with your studies.

- Andrew

Today's production of biofuels derived from corn or palm oil crop varies depending on geographical location, agricultural practices, and market demand. Both corn and palm oil are used in the production of biofuels, particularly biodiesel, but the prevalence of each feedstock can differ by region.

In the United States, for instance, corn-based ethanol is a common biofuel produced in large quantities, with numerous biodiesel plants that utilize corn as a primary feedstock. This is due to the abundance of corn crops and the established infrastructure for its processing. Corn-based ethanol is widely used to blend with gasoline and reduce greenhouse gas emissions.

On the other hand, palm oil is a significant feedstock for biodiesel production in regions where palm trees are cultivated, such as Southeast Asia. Palm oil biodiesel has gained popularity in these areas due to its high energy content and efficiency in biodiesel production. However, the environmental impact of palm oil cultivation, including deforestation and habitat destruction, has led to concerns and calls for sustainable practices.

If you are looking for biodiesel plant manufacturers, you can search for them online or contact industry associations and directories related to biofuels and renewable energy. These manufacturers design and build biodiesel plants, providing equipment and technology for the production of biodiesel from various feedstocks, including corn and palm oil. It's essential to consider the sustainability and environmental implications of the chosen feedstock when planning a biodiesel production facility, as this can have a significant impact on public perception and regulatory compliance.

Understanding the argument - ­
Today's production of biofuels derived from corn or from palm oil crops threatens global food supplies—the United States' push for ethanol has already contributed to rising world market prices for corn—and furthermore prompts eager farmers to carve out new farmland from dwindling rain forests. - Background info. It highlights two issues:
a. Threatens global food supplies
b. Prompts farmers to carve out new farmland from dwindling rainforests. 

For these reasons, experts now recommend cultivation of the jatropha plant, whose seeds contain up to 40 percent oil. - So, to counter the two issues, experts recommend cultivating the jatropha plant (by the way, Jatropa's plants contain up to 40% oil).

Jatropha and jatropha oil are inedible, so using this oil to manufacture a biofuel will not diminish current global food supplies. And, because the plants favor hot, dry conditions, they are unlikely to threaten rainforests. - So, in these two sentences, the author counters the two issues by the Jatropha plant. How?
a. Threatens global food supplies - Jatropa and Jatropa oil are inedible. 
b. Prompts farmers to carve out new farmland from dwindling rainforests. - They favor hot and dry conditions. 

Which of the following would, if true, most undermine the rationale provided above for recommending cultivation of jatropha for biofuel manufacture?

Question - What rationale? The reasons provided to counter the two issues. 

A. Cultivation of jatropha plants in wet climates, though possible, is costly. - Touches neither of two issues. Out of scope. 

B. Some people believe that jatropha oil has medicinal value. - First, "some" can be at least 1. But that's not the problem here. It touches neither of the issues, i.e., it Threatens food supplies, and further dwindles the rainforest. Out of scope. 

C. One acre of jatropha plants yields 20 percent less oil than one acre of palm trees. - While this option talks about an important point in general that points towards needing more land to plant Jatropha, we know nothing about the kind of land used - marginal or non-marginal. The additional problem here is that neither of the two issues is discussed. It doesn't discuss "threatening global food supplies because it is inedible" and "prompting farmers to use dwindling rainforests because it favors dry conditions." 

D. The growing conditions favored by jatropha plants are ideal for a number of food crops. - This directly weakens the first issue (threatens the food supplies even if they are inedible) because it says that the growing conditions, land, climate, etc., are similar to many food crops. Farmers can stop producing those large numbers of food crops and shift to Jatropha, a strategy detrimental to food supplies.

"The phrase "a number of" is commonly used in English to indicate that there are several, many, or multiple instances of something. It's used to refer to an unspecified but significant quantity or amount. The exact number is not specified and can vary widely based on the context. For example, saying "a number of people attended the event" implies that there was a sizable but unspecified group of attendees."

E. The world market price of petroleum-derived fuels has fluctuated widely, sometimes falling below the world market price of any biofuel. - out of scope. Talks about neither of the issues. ­