The correct answers are was discovered and is kept.
"Was discovered" is the past simple passive. We use it because the action happened at a specific time in the past (1842), and the diamond received the action (it didn't discover anything itself).
"Is kept" is the present simple passive. We use it because this is a general fact or current state ("Today"), and the diamond is receiving the action of being kept.
Passive voice
If your writing has been called "weak" or "evasive" — Mistakes were made, It was decided that... — you've hit the passive voice's main pitfall. Used deliberately, the passive is precise and useful: it foregrounds the action when the doer doesn't matter. Used by default, it makes prose feel like nobody's responsible for anything.
The passive voice is formed with be + past participle and turns the object into the subject: The chef cooked the meal → The meal was cooked (by the chef). Useful when the action matters more than the doer; overused, it makes writing feel evasive.
Present tense
If you've ever told someone I am living here for ten years (should be have lived or have been living) — you've hit the present perfect's main puzzle. English insists that "started in the past, still true now" lives in the present perfect, not the simple present. Internalise that one rule and a whole class of common errors disappears.
The present tense in English has four forms: simple present (I work) for habits and general truths; present progressive (I am working) for now or temporary; present perfect (I have worked) for past with present relevance; present perfect progressive (I have been working) for ongoing duration up to now.
Past tense
If you've ever told a story in English and felt the timeline get tangled — I came home, the dog ate, the cat slept — you've hit the limits of using simple past for everything. The past tense system has four forms specifically because real stories have layered timing: things that happened before other things, actions caught in progress, sequences of completed events.
The past tense has four English forms: simple past (I walked), past progressive (I was walking), past perfect (I had walked — earlier than another past event), past perfect progressive (I had been walking — ongoing up to a past point). Plus irregular verbs for the simple-past form.
Simple tense
If you're at A1/A2 and the array of English tenses feels overwhelming, here's the good news: most of what you need to say at the start fits in the simple forms. I work, I worked, I will work — three forms cover habits, completed past actions, and basic future. Master these first; the progressive and perfect come more easily once the simple is solid.
The simple aspect is the unmarked verb form — no progressive -ing, no have + past participle. I go, I went, I will go. Marks single completed actions, habits, or permanent states.
B1 | Intermediate
If you can hold a conversation about your weekend, explain why you're late, and follow a short news story without panicking — but still feel lost in fast or technical English — you're probably operating at B1. Knowing this matters: study material at the wrong level either bores you or burns you out, and B1 is the typical target for travel, casual work, and most everyday social English.
B1 is the intermediate level in the CEFR framework, where you handle everyday English independently and start combining ideas with complex sentences, passive voice, and modal verbs.
Difficulty: Medium
If easy questions feel too obvious but hard questions leave you guessing, you're probably ready for Medium — the level where most real learning happens. It pushes just enough to expose the rules you don't quite have yet, without burying you in edge cases. This is where steady fluency is built, one well-aimed challenge at a time.
The Medium difficulty tag marks middle-range challenges — typically A2 to B1. One rule per question, realistic distractors, and contexts that require active thought rather than instant recognition.