Final answer:
Option 3 most effectively combines the initial sentences while maintaining their meaning. It reads smoothly and preserves the context of the lemon tree usually being covered with fruit.
Step-by-step explanation:
The most effective way to combine the sentences 'Yesterday, I drove to work past the lemon tree' and 'It was, as is usual, covered with fruit' at the underlined portion is:
Option 3: I drove to work past the lemon tree, which is usually covered with fruit.
This option effectively combines the two original sentences into one smooth and coherent sentence without changing the meaning or context. It clearly explains that the occurrence of the lemon tree being covered with fruit is a usual phenomenon.