I think E.
Since some sycamores are younger than maples which are younger than tulips(A majority, but not all, of the garden’s sycamores are older than any of its maples), those sycamores must be younger than youngest tulips (E).
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Definitely E

For these types of questions, I think you need to jot stuff down to track the logic.

1. ALL TULIPS older than ANY MAPLE
2. MAJORITY (though not all) SYCAMORE older than ANY MAPLE (This is where you should focus on)
3. ALL MAPLE older than ANY DOGWOOD

Running through the list of options C and E are the only ones that address that subset of the Sycamore population that does not constitute the majority older than ANY MAPLE.

(C) Some sycamores are not as old as the oldest dogwoods.
(E) Some sycamores are not as old as the youngest tulip trees.

Based on E, can we conclude that some syc are not as old as the youngest tulip - yes because we know that some maples are older than some sycamores and all tulips are older than maples, therefore some sycs <maples
Based on C can we conclude that some syc are not as old as the oldest dogwood, - maybe but not 100%. Remember this is a must be true question.

To even make things clearer assume the following

Minimum age of Tulip (16)
Minimum age of Maple (14)
Minimum age of Sycamore (13) - this is the subset that is younger than the Maple remember
Minimum age of Dogwood (13)

Based on the above, are some sycamores are not as old as the oldest dogwoods (maybe, maybe not). Conversely, are some sycamores not as old as the youngest tulip trees - 100% YES - This is the answer, there are no doubts.

Lets get the facts.

1. All tulips are older than maples.
2. Majority sycamores are older than maples.
3. All maples are older than dogwoods.

Now lets see the options provided:

Option A: Not possible from 1 and 2.
Option B: Might be possible from 2 and 3. But need not be true.
Option C: Might be possible from 2 and 3. But need not be true.
Option D: Might be possible from 1 and 2. But need not be true.
option E: Possible from 1 and 2. Some syncamores are not as old as maples. And all tulips are older than maples. Hence, follows E.

I go with E.

Hope it helps. Whats the OA?

Thanks all, OA is E

I like the explanation on E