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It is plural of alumna meaning young women who are graduates or former students of a specific school, college, or university.

'Time and tide' is a compound subject with two nouns, so it takes the plural verb 'wait,' not 'waits.' This proverb means that neither time nor the changing circumstances of life stop for anyone. The plural form emphasizes that both time and tide are distinct forces that don't wait.

The subject 'All I want' functions as a singular noun phrase because the core subject is 'I' (first person singular). In present tense, 'I want' agrees with 'is', not 'are' or 'were'. The phrase 'All I want' means 'everything that I desire', which is a singular concept.

The phrase 'a series of' is a collective noun phrase that takes a singular verb. Even though 'sightings' is plural, the true grammatical subject is 'series' (singular). This is why 'has' (singular) is correct, not 'have' (plural).

Academic discipline names ending in '-ics' (economics, physics, mathematics) take singular verbs when referring to the field of study itself. When referring to plural specific phenomena, they might take plural verbs, but here it's clearly the discipline, so 'is' is correct.

The main subject is 'The depletion' (singular). Phrases starting with 'in addition to' are parenthetical and don't change the number of the subject. Therefore, the verb must be singular 'has', not plural 'have'. 'Would' and 'could' are grammatically incorrect - present perfect 'has encouraged' is the right tense.

The true subject is 'Your blood pressure' (singular). The phrase 'as well as your temperature and heartbeat' is additive but doesn't make the subject plural. Therefore, the verb must agree with the singular 'blood pressure', taking 'is' not 'are'. 'Was/were' are wrong because the context suggests current state ('today').

If the subsequent clause is in the past perfect, the antecedent is in the present perfect. 

We use the Third Conditional to talk about 'impossible' conditions, impossible because they are in the past and we cannot change what has happened.If the antecedent is in the past perfect tense, the subsequent must be in present perfect. If you had, I would have...

In the case of 'wish' we always use 'were'. 

Usage of past perfect in the antecedent leaves no scope for any other option than option 2.  

In conditional sentences if there is 'would' in the subsequent clause, we use past form of the verb in the antecedent. 

Here the antecedent 'were' is not indicative of past indefinite but of a 'wish', the subsequent 'would' follows such wishes.  

If the antecedent is in the past indefinite, the subsequent must be in the present perfect. 

Here 'were' shows a fact (present). In such cases we use 'would/wouldn't' + first form of the verb.