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此题不能用when，原题中when引导的not accompanied by corresponding increases in sales不是一定会发生的情况。
贴上Manhattan Ron关于when/if的解释：
If your "conditional sentence" depends on something that occurs at a specific time, then "when" can be used to express the whole conditional idea.
You can't use when if ... 1. Something is NOT an event that occurs at a specific point in time。 Ex: If you are a woman, the older executives may not speak to you as honestly as they will to me. ("When you are a woman" is nonsense, unless someone has the ability to change back and forth between sexes.) 2. The consequence doesn't occur at the time of the conditional part Ex: If you smoke cigarettes, you will die of cancer. "When you smoke cigarettes" doesn't work here, since you won't die when you smoke the cigarettes"”you'll die decades later.
If the time relationship is appropriate, though, "when" is more descriptive than "if", because it's more precise. Ex: When you return the goods, you'll receive a refund. You'll receive your refund at the time when you return the goods"”i.e., not later. Ex: If you return the goods, you'll receive a refund. This sentence is more vague about the timeline. You might get the refund when you actually return the goods"”but you might get it much later.
The primary difference between "if" and "when" is that "when" implies that the precipitating event will definitely happen. Ex: When I eat white rice, I can easily eat too much, because pure starch isn't filling. If I eat white rice, I can easily eat too much, because pure starch isn't filling. These two sentences express the same possibility of overeating. The difference is that the first one ("When I eat white rice") implies that there are definitely occasions on which I eat white rice, while the second one makes no such implication. I could make the second statement even if I know I'll never eat white rice again. | 
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发表于 2011-3-4 22:41:13
