Grammar: Tenses

詳解：The phrase 'by the time she arrives' refers to a future point, and 'for two hours' indicates duration up to that point. The future perfect continuous (will have been waiting) is used to emphasize the duration of an action that will be in progress before another future time. Option B (will have waited) is possible but less natural as it emphasizes completion rather than duration. Options A and D are incorrect because they do not show the action continuing up to a future time.

詳解：The present perfect (have lost) is used to describe a past action with a present result—the keys are still missing. Option A (lost) is simple past, which does not connect to the present. Option B (was losing) is past continuous, implying an ongoing action in the past. Option D (had lost) is past perfect, which would require another past event to reference.

詳解：The past perfect (had lived) is used to show that an action was completed before another past action (moved to Paris). Option A (lived) is simple past, which does not establish the sequence clearly. Option B (has lived) is present perfect, which is not used with a past reference point. Option D (was living) is past continuous, which emphasizes duration but not completion before another event.

詳解：The future continuous (will be studying) is used to describe an action that will be in progress at a specific future time. 'At this time tomorrow' indicates a specific moment, so the continuous form is appropriate. Option B (will study) is simple future, which does not emphasize the ongoing nature. Options A and D are incorrect because they do not refer to the future.

詳解：The simple past (went) is used for a completed action in a specific past time period (last month). Option A (goes) is present simple, which is for habits or general truths. Option C (has gone) is present perfect, which connects to the present. Option D (had gone) is past perfect, which would need a later past event to reference.

詳解：The past perfect (had known) indicates that the knowing happened before the decision (past action). Option C (have known) is present perfect, which does not fit with the past 'decided'. Options A and B are simple present/past, which do not show the sequence clearly.

詳解：The present continuous (am cooking) is used for an action happening at the moment of speaking. Option A (cook) is simple present, used for habits. Option C (have cooked) suggests completion. Option D (cooked) is past tense, which does not fit the current situation.

詳解：The future perfect (will have worked) is used to express that an action will be completed before a specific future time (the end of this year). Option B (will work) is simple future, which does not show completion. Options A and D are present tenses, incorrect for a future deadline.

詳解：The past continuous (were waiting) describes an action in progress when another action (arrived) occurred. Option B (waited) is simple past, which could imply they waited after I arrived. Option D (had waited) is past perfect, which would mean they waited before I arrived. Option A is present tense.

詳解：The present perfect (have read) is used for an experience that happened at an unspecified time in the past and is relevant now (still love it). 'Already' often accompanies the present perfect. Option A (read) is simple past, which would be used for a specific past time. Option C (had read) is past perfect, requiring another past event. Option D (was reading) is past continuous, which does not indicate completion.