Step 1 : Understanding the Question
This question tests the ability to use logical connectors and conjunctions to join two contrasting ideas. The sentence describes two states of desert flowers: being "invisible for years" (an unusual condition) and "appearing suddenly" (a rapid change). We must find the word pair that provides the correct emphasis and logical transition between these two states.
Step 2 : Detailed Explanation
Analyzing the Context: Desert flowers are seeds that stay dormant. The phrase "invisible for years" is a surprising truth. The phrase "appear suddenly" is the contrast to that invisibility.
Evaluating Option (A) - alternatively or: "Alternatively" is used to suggest a different choice between two things. "Or" also suggests a choice. Since the flowers do both (wait and then appear), they aren't choosing one over the other; this option is logically incorrect.
Evaluating Option (B) - consequently and: "Consequently" means "as a result." Invisibility isn't what *causes* them to appear; the rain is the cause. Therefore, "consequently" creates a false causal link.
Evaluating Option (C) - nevertheless, so: "Nevertheless" could show contrast, but "so" implies that they appear *because* they were invisible. This doesn't capture the biological reality of the rain being the trigger.
Evaluating Option (D) - actually, but: This is the correct choice. "Actually" emphasizes the surprising fact that they remain hidden for years. "But" is the perfect connector to show the sharp contrast between their long invisibility and their sudden appearance.
Step 3: Final Answer
The most natural and logical way to complete the sentence is by using "actually" to reinforce the first clause and "but" to introduce the contrast in the second clause. Thus, option (D) is correct.