This sentence clearly is contrasting the size of the seed to the size of the tree. This helps you to eliminate "lovely," "beautiful," and "healthy." Also, it was so large, that few had expected it to be so big. Therefore, the best choice is "gigantic", which expresses this way of being very big—in contrast to the seed's original tiny size.

The key expression in the sentence is not in good enough shape. This means that the runner did not prepare enough to be in good shape for race day. Therefore, his or her training was not sufficient.  To "suffice" means to be enough. The opposite of something that is sufficient is something that is insufficient.

The second sentence is key to understanding this question. The young man can't figure out where the water is coming from. He is looking for its origin or its "source." He certainly knows its location and its place! What is annoying to him is the fact that he can't figure out where it is coming from!

This sentence sets up a contrast. The first half of the sentence discusses how we can learn to do many things "sufficiently well." This means that we can learn how to do these things well enough. We can, however, only become experts at a few things.  Thus, the word "excel" is the best option. This is a verb meaning roughly to do very well or with a great deal of skill.

This sentence hints at an intensification. It says that Don was "not just mildly glad." This means that he was not merely glad in a minor way. No! He was very glad, meaning that he rejoiced greatly. Use this adverb to express the intensification indicated by the clues.

At least when this sentence is read in its most literal sense, it seems that Lawrence is trying to guess or calculate the time it will take for him to complete the job. This interpretation is helped by the fact that the second sentence says that it will help him to figure out his schedule. When we try to make an educated or intelligent guess about something—for example, time or costs—we "estimate" that thing. That is what Lawrence is doing in this sentence.

The sentence merely states that Nigel liked talking for a long time with his friends. Therefore, do not read too much into the sentence. It does not tell us that he liked arguing with them or even that he liked to debate them. The best option is the simplest in this case—"conversation."

Notice in the second sentence that it is admitted that some older people are afraid of new technology. The implication here, however, is that it is unfair to think that this applies in general to all older people. Instead, many use technology with enjoyment and skill. A stereotype is a kind of unfair idea that may be true in some limited way but is not absolutely true. 

The second half of this sentence provides a justification for John's action. From good motives, he took the money from his brother. It seems that everyone overlooked this fact and was judging him negatively. Now, likely everyone was treating him like an outcast or as a criminal. The best option will be one that describes the fact that John had taken the money. Thus, it would seem best to say that everyone treated him as thief. Try to keep your words as close as possible to the context when answering questions like this. You will not always have to do this, but in questions like this one, it makes all the difference!

For this sentence, you are lucky to have Egbert's motto. He didn't want to do anything extra, so he wanted to do a minimal amount of work. The word "minimum" can be used as an adjective to mean "the least". Thus, Egbert wants to do "just enough" to get by with a passing grade.